Your US mid-term elections daily digest

There are just under four weeks until the US elections that will help define the rest of Donald Trump's presidency.

The mid-term elections will see people vote for members of both houses of Congress, as well as for governors in 36 out of 50 states.

Between now and then, we'll bring you updates and all the best analysis every weekday in this round-up.

Today we have another New York billionaire making a splash, a court ruling on voting in a key Senate race and a Ferris Bueller moment.

One mogul to watch

Former New York Mayor Michael Bloomberg just registered as a Democrat

Former New York Mayor Michael Bloomberg - who pledged in June to spend $80m on Democratic candidates in the midterm elections - has registered as a Democrat.

In an Instagram post on Wednesday, he said he was made the decision "because we need Democrats to provide the checks and balance our nation so badly needs".

Mr Bloomberg won mayoral elections in New York as a Republican and Independent, and has flirted with presidential runs in 2008, 2012, and 2016, but never threw his hat into the ring.

Last month he told CNN he was considering running for president in 2020, but added: "Right now, I'm only focused on the midterms."

Mr Bloomberg, who earned a fortune as the founder of media and finance company Bloomberg LP, has recently backed progressive issues such as gun control, but has opposed liberal lawmakers' efforts to further regulate big banks and businesses.

He has also spoken in favour of "stop-and-frisk," which permits police to randomly search people - another policy that some Democratic voters may find unpalatable.

"It's impossible to conceive that I could run as a Republican - things like [abortion] choice, so many of the issues, I'm just way away from where the Republican Party is today," Mr Bloomberg told the New York Times in September.

"That's not to say I'm with the Democratic Party on everything, but I don't see how you could possibly run as a Republican."

A New York business tycoon running for office... now that's a novel thought.

One race to watch

North Dakota's Native Americans do not always have ID: that could pose a problem

One Senate seat Republicans hope to flip is in North Dakota, where the Democratic incumbent Heidi Heitkamp won by just under 3,000 votes in 2012.

Flipping North Dakota would give Republicans a huge advantage in keeping control of the Senate (given that there are only nine Republican seats in contention this year, Democrats have no margin for error if they want to claim the Senate).

With this in mind, a US Supreme Court ruling on Tuesday could have profound implications.

Justices backed a lower court ruling that required voters in North Dakota to show forms of identification and proof of residential address if they wanted to vote in the mid-terms.

The appeal that came before the court said that up to 70,000 people in the state did not have ID and therefore would not be able to vote (up to 20% of the electorate).

Heidi Heitkamp is facing a fight to keep her Senate seat in North Dakota

Why does this matter?

Well, in 2012, North Dakota's Native Americans voted heavily in favour of Heitkamp (in Sioux County, for example, 84% of voters backed her over her Republican counterpart).

Because Native Americans often lack a street system, they commonly use PO Box addresses, and so often don't have proof of residential address.

In an interview with the West Fargo Pioneer last week, Heitkamp said the ID requirements "clearly target" Native Americans and college students.

• Your simple guide to the mid-terms

Right now, she needs all the support she can get - two weeks ago, she changed her mind on approving Donald Trump's Supreme Court nominee, Brett Kavanaugh, and voted No, provoking a backlash from Republicans. And polls suggest she is slipping further and further behind Republican Senate contender Kevin Cramer.

(By the way, Justice Kavanaugh did not take part in the Supreme Court decision on Tuesday).

One quote

On the subject of Justice Kavanaugh, it's pretty clear by now that his name is being used as a rallying cry by Republicans ahead of the mid-terms.

His confirmation process, in which he denied sexual assault in the face of testimony by accuser Christine Blasey Ford, saw Democrats voice support for her and demand a more detailed investigation.

• Should Trump be worried by mid-terms?

As we noted on Monday, that confirmation process has actually helped the GOP reverse (or at least slow) momentum the Democrats had in key races all summer.

And now, in a speech on Tuesday night in Iowa, the president has made a direct link: for Republicans, these mid-terms are a referendum on the way Democrats acted around Kavanaugh.

One video to watch

This clip posted on Twitter by MSNBC's Jacob Soboroff has been widely shared over the past few hours.

It was filmed in Orange County, California, which has four Republican-held seats in the House of Representatives.

Democrats hope to flip those seats, and would need a strong youth vote to do so. There's just one problem, as Soboroff's interviews show...

Always good to have a Ferris Bueller reference.

We'll talk more about the role of the youth vote in a later digest.

One feud to follow

Ye and Tay-Tay in happier times

There's a risk of turning this round-up into a daily Taylor Swift digest but her statement of support for Democratic candidates this week has mixed things up in an interesting way.

Swift's shout-out for people to register to vote (which she repeated at the American Music Awards on Tuesday night) has led to a significant uptick in registration.

Her comments have also threatened to reignite one of music's least likely on-again-off-again feuds, between Swift and avowed Trump supporter Kanye West, who will meet the president later this week.

Here's our brief history of their beef, that is now being taken into the political arena.

Pop stars calling on people to register is clearly now a thing, by the way - Rihanna has followed suit.