Following the second vote, Chief Justice Roberts, who presided over the Senate trial, announced that President Trump had been acquitted on the second article of impeachment - obstruction of Congress.

"Donald John Trump, President of the United States, is found not guilty," Roberts said.

This second vote fell exactly along party lines - all Democrats voted to convict and all Republicans voted to acquit: 53-47.

"The Senate having voted, and two-thirds of the Senate not having found him guilty," Roberts said. "It is therefore ordered and adjudged" that the president is acquitted on both charges of impeachment.

President Trump has been acquitted on the second impeachment charge, obstruction of congress, by a vote of 53 to 47.

Unlike the first, this vote was partisan - all Democrats voted to convict and all Republicans voted to acquit.

Trump has now been acquitted in his impeachment trial, as expected. He is the third US president in history to face and survive a Senate trial.

The second roll call vote of the day, on the charge of obstruction of Congress, is now underway in the chamber.

Christian Fraser
BBC News

It was striking, although this was a foregone conclusion, how one senator changed the tone and the mood of the day. Romney will be vilified.

And although this was a foregone conclusion, this has only happened three times. As the clerk read out the guilties - 48 guilties - it underlined just how serious this vote was for the president.

After the first vote, Chief Justice Roberts announced that the president was "not guilty as charged on the first article of impeachment" - abuse of power.

Forty-eight senators voted to convict, falling short of the two-thirds majority to remove the president from office.

A Senate clerk is now reading the charges for the second article of impeachment - obstruction of Congress.

President Trump has been acquitted on the first impeachment charge, abuse of power, by a vote of of 52 to 48.

All Democrats and one Republican - Mitt Romney - voted against the president.

The Senate is now holding a roll-call vote.

The clerk is reading each senator's name.

When it is their turn they are responding either "guilty" or "not guilty".

The Senate clerk is now reading out the first charge against the president: abuse of power - alleging that Trump sought to influence Ukraine to open investigations that would help him politically.

After the clerk finishes speaking, the senators will cast their first impeachment votes, by roll call.

Image source, Caroline Brehman/CQ-Roll Call, Inc via Getty Images

West Virginia Senator Joe Manchin has said he will vote to convict President Trump on both articles of impeachment.

The Democrat was being closely watched by fellow party-members - Manchin is a moderate Democrat who has voted with Republicans in the past, and his state is seen as leaning conservative.

"Voting whether or not to remove a sitting President has been a truly difficult decision... I have reached my conclusion reluctantly," Manchin said in a statement.

"The President is not entitled to act with blatant disregard for an equal branch of government or use the superpower status of the United States to condition our support of democracy and our allies on any political favor."

He continued: "I must vote yes on the articles of impeachment. I take no pleasure in these votes, and am saddened this is the legacy we leave our children and grandchildren."

With Manchin's announcement, it looks like all Senate Democrats will vote to convict.

Mitch McConnell closed his speech to the floor by accusing Democrats of caving in to a "toxic temptation" and waging "war on the traditions themselves".

"Is this really where you wanna go?" he said. "The president isn't really the president and acquittal isn't really acquittal?"

The chamber is now in recess until senators begin to vote shortly on whether to convict Donald Trump.

Republican Senate majority leader Mitch McConnell is addressing the chamber.

"This partisan impeachment will end today," he said. "But this partisanship," he added, "will not".

He accused Democrats of refusing to accept the 2016 election.

"Normally when a party loses an election it accepts defeat, but not this time," he said.

"They still don't accept the American voters' last decision, and now they're preparing to reject the American voters next decision if they don't like that one - heads we win. Tails you cheated."

Image source, Tom Williams/CQ-Roll Call, Inc via Getty Image

Arizona Democratic Senator Kyrsten Sinema will vote to convict Trump, external, according to reports in Arizona media.

Sinema won a tight race in 2018 from a Republican, and was one of a handful of Democrats being watched for a possible vote with the president.

Image source, MANDEL NGAN/AFP via Getty Images

From the Senate floor, Minority Leader Chuck Schumer derided what he described as the "sham trial" of Donald Trump in the Senate.

The chamber had "conducted the least fair, least thorough, most rushed impeachment trial in the history of this country," the New York Democrat said, accusing Republicans of standing in the way of a fair process.

"The verdict of this kangaroo court will be meaningless," Schumer said.

He said the president would boast he had been totally total exonerated, "but we know better".

Jonathan Turley
Professor of constitutional law, George Washington University

I thought it was an excellent speech [by Romney]. I don't think anyone who has had even passing interactions with Senator Romney doubts his veracity. I think he has taken his vote very seriously and he has fulfilled his oath as he believes it must be fulfilled.

It's a decision that could very well put a lot of pressure on Senator Susan Collins [a moderate Maine Republican]. She has already indicated she will not vote to convict and will vote to acquit. For that, she may be getting blowback in her state.

Now that one Republican has broken ranks, this is technically a bipartisan effort to convict the president.

I was glad to see that Senator Romney rejected the second article of impeachment, dealing with obstruction of Congress. This is the article I testified against most vociferously in the House. I thought this was a very flawed article.

It's now possible that a couple of Democratic senators might be troubled by Article Two and may join Republicans in voting to acquit him on that article.

Jon Sopel
BBC North America Editor

Mitt Romney's bombshell speech won't alter the outcome of this trial - Donald Trump will be acquitted.

But what it does is deprive the president of an important boast - one that he's made again and again: that the Republican Party stands united against a partisan hoax got up by the Democrats.

Carefully and precisely, the senator from Utah set out the case against Donald Trump.

"The grave question the Constitution tasks senators to answer is whether the president committed an act so extreme and egregious that it rises to the level of a high crime and misdemeanour."

And then after a short pause, he says: "Yes, he did."

He concluded that what the president had done in his dealing with the Ukrainians had been motivated by personal and political gain - and for that reason, he was guilty of "an appalling abuse of public trust".

In the hyper-partisanship of today’s Republican party, where fealty to Donald Trump is all-important, Romney will be vilified.

And he knows it. But he's done this with his eyes wide open.

And not an ounce of regret.

Image source, Getty Images

Image source, Getty Images

Mitt Romney may not be the only senator to cross the aisle today. A couple of Democrats in Republican-leaning states might also defect, to guard against angering their voters. Any defections would hand Trump a symbolic win that would allow him to say he was acquitted in a bi-partisan vote.

Here are two key Democrats to watch:

Joe Manchin, West Virginia

Manchin is a moderate Democrat who has voted with Republicans in the past. His state is seen as leaning conservative. Following the closing statements of the trial earlier this week, Manchin called for legislation to censure Trump over the Ukraine matter (a mostly symbolic move).

"Censure would allow this body to unite across party lines," Manchin said. "[Trump's] behaviour cannot go unchecked by the Senate and censure would allow a bipartisan statement condemning his unacceptable behaviour in the strongest terms."

Krysten Sinema, Arizona

Sinema, like Manchin, hails from a more conservative region and is a party moderate.

She won her seat from a Republican in a tight race during the 2018 mid-term elections and became the south-western state’s first Democratic senator since 1994.

Image source, Getty Images

Ronna McDaniel, the Republican National Committee party chairwoman and Mitt Romney's niece, said she “disagreed” with her uncle’s decision, adding that she thought the president had done "nothing wrong".

Image source, Getty Images

The president's eldest son has condemned Mitt Romney, saying the senator and former Republican presidential candidate was "officially a member of the resistance & should be expelled" from the party.

"Mitt Romney is forever bitter that he will never be POTUS," Donald Trump Jr tweeted, using an acronym for President of the United States of America.

"He was too weak to beat the Democrats then so he’s joining them now."

Meanwhile, his brother Eric is plugging Trump branded wine for Valentine's Day.

Given the expected acquittal, a number of anti-Trump protests have been scheduled across the country.

Several protesters chanting "Trump is guilty, honour your oaths” were arrested inside the Capitol rotunda in Washington on Wednesday.

More protests are planned for the evening to coincide with the vote.

The immediate reaction to Romney's announcement on conservative Twitter ranged from respectful disagreement to bitter condemnation.

But for the most part, there seemed to be a consensus among conservative commentators: Conviction is the wrong decision.

Those weighing in included Fox News political contributor Guy Benson, defence attorney (and avid Trump supporter) David Wohl, and podcast pundit Ben Shapiro.