Image source, SAUL LOEB/AFP via Getty Images

It was a brief, but historic appearance by House Speaker Nancy Pelosi and other top Democrats.

Pelosi, New York Congressman Jerrold Nadler and California Congressman Adam Schiff outlined the two articles of impeachment - abuse of power and obstruction of Congress - and did not stay for questions.

As BBC's Jon Sopel writes, the charges were expected, but nonetheless momentous.

A little lost? We have you covered. Here's what you need to know about impeachment and Trump.

Intelligence Chairman Adam Schiff said Trump "seemed to abrogate the power of Congress to hold him accountable", referring to the White House refusal to co-operate with the congressional probe.

"His abuse of power has left us no choice. To do nothing would make ourselves complicit," Mr Schiff said.

His talks with Ukraine "undermined our national security," Schiff added. To do nothing could allow coming leaders to be "as corrupt, or malfeasant or incompetent as they like with no prospect" of ever being held to account.

"He still wants Ukraine to intervene in our election to help his campaign," he said, adding that the president's personal lawyer Rudy Giuliani was still in Ukraine investigating former Vice-President Joe Biden.

Democrats say Trump dangled two bargaining chips - $400m (£309m) of military aid to Ukraine that had already been allocated by Congress, and a White House meeting with Ukraine's new leader.

They think this political pressure on a vulnerable US ally amounts to an abuse of power.

The first investigation Trump wanted from Ukraine was into one of his main Democratic challengers, Joe Biden, and his son Hunter.

Hunter joined the board of a Ukrainian company when Joe Biden was US vice-president. The second Trump demand was that Ukraine try to corroborate a conspiracy theory that Ukraine, not Russia, interfered in the last US presidential election.

This theory has been widely debunked, and the US intelligence agencies are unanimous in saying Moscow was behind the hacking of Democratic Party emails in 2016.

Image source, SAUL LOEB/AFP via Getty Images

Chairman of the House Judiciary Committee Jerrold Nadler formally announced the two articles of impeachment filed against President Trump: abuse of power and obstruction of Congress.

Trump's "efforts to solicit foreign interference in the 2020 election" "compromised our national security and threatened the integrity of our elections," Nadler says.

Trump has denied all wrongdoing.

"We must take this solemn step today," Nadler says.

The integrity of our next election is at risk, from a president that has already sought foreign interference.. and has consistently put himself above country."

Image source, SAUL LOEB/AFP via Getty Images

At a news conference in Washington, Democrats are now unveiling charges against Trump.

They are describing the president as a "danger" to US democracy, and saying that they must urgently remove him from office.

Democrat leaders of the various House committees are holding a news conference to explain the charges against Trump.

Among those participating are:

• New York Congressman Jerrold Nadler
• California Congressman Adam Schiff
• New York Congressman Eliot Engel
• California Congresswoman Maxine Waters
• New York Congresswoman Carolyn Maloney

Trump has refused an invite from House Democrats to participate in the impeachment hearings. Instead, he's meeting on Tuesday with Russia's top diplomat, Sergei Lavrov, who is visiting Washington.

Declining the invite, White House lawyers called the inquiry into the president "completely baseless" and accused Democrats of violating "basic principles of due process and fundamental fairness".

So Trump won't be there - but it looks like he's already tuning in on Twitter.

Before today's events began he had sent out three tweets on the probe, dismissing the inquiry as "sheer political madness".

Image source, Russian foreign ministry

Image source, Salwan Georges/The Washington Post via Getty Images

The president is accused of breaking the law by pressuring Ukraine's leader to dig up damaging information on a political rival.

In July, he urged his Ukrainian counterpart to investigate one of the frontrunners to take him on in next year's presidential election. This matters because it is illegal to ask foreign entities for help in winning a US election.

An impeachment inquiry that could see the president eventually removed from office is under way.

But there is a fierce debate about whether Trump broke the law or committed an impeachable offence - he himself says he has done nothing wrong.

Want more detail? Read the full story here.

Image source, Getty Images

Democratic Speaker of the House Nancy Pelosi has tweeted ahead of the formal announcement of articles of impeachment.

Her tweet comes one day after a lawyer for her party argued that Trump presented "a clear and present danger" to the upcoming US presidential election, which is now less than a year away.

Democrats worked in Pelosi's office late into Monday night, but she has not yet confirmed that she has enough votes in the House to impeach Trump.

"On an issue like this, we don’t count the votes. People will just make their voices known on it," Pelosi said at The Wall Street Journal CEO Council event on Monday.

Image source, Sarah Silbiger/Getty Image

Welcome to our live coverage of the impeachment investigation into President Donald Trump.

Today, Democratic lawmakers in the House of Representatives will formally unveil two articles of impeachment, charging Mr Trump with obstructing Congress and abuse of power.

Democrats allege Mr Trump used his office to pressure Ukraine's leader to launch investigations which would benefit him politically, putting himself over his country.

The White House has refused to participate in the House inquiry and has denied any wrongdoing, calling impeachment a political drama intended to hurt Mr Trump in his 2020 re-election bid.

The articles will be voted on in the full House of Representatives, and if passed, will move to the Senate for a trial.