But, wait! It’s possible that Mitch McConnell, the Senate majority leader, could refuse to hold a trial — a move that would overturn long-held Senate rules but might not be unconstitutional.

How long will this all take?

As long as House Speaker Nancy Pelosi wants.

But there’s a strong political argument for moving the process forward this year, given that it gets harder for Democrats to make their case as the election nears — and voters could throw Mr. Trump out of office anyhow. Historically, the process has taken about four months.

How likely is it that Mr. Trump will be removed from office at the end of all this?

Not very. There are no signs that Senate Republicans have any appetite for investigating Mr. Trump. To reach a two-thirds majority in the Senate, at least 20 Republicans would have to vote with every Democrat to remove Mr. Trump from office.

No House Republicans and only two Senate Republicans back any kind of investigation into Mr. Trump. Here’s how Senator Mitt Romney of Utah, who described the allegations against Mr. Trump as “deeply troubling,” explained his party’s resistance earlier this week:

There’s such enormous power associated with being the party in power, both in the White House as well as in the Senate and the House. … I think it’s very natural for people to look at circumstances and see them in the light that’s most amenable to their maintaining power, and doing things to preserve that power.

How does this effect the 2020 election?

This clearly leads to a Joe Walsh surge in Arizona, a Joe Sestak victory in North Dakota and Mayor Pete Buttigieg dropping out of the race to become a professor of 16th century art history.

Seriously, though, no one really knows.

As my colleague Reid Epstein and I wrote today, it’s probably not great for the lower-polling candidates, who will now face an even greater struggle to get media attention.

How it impacts the front-runners in the race — Mr. Biden and Senator Elizabeth Warren — is a topic of great debate within Democratic circles right now. We’ve never seen an impeachment inquiry quite like this, leaving the candidates, strategists and assorted prognosticators navigating uncharted political waters.

Also important to remember: Mr. Trump can run for re-election even if he’s impeached by the House. And maybe even if he’s removed by the Senate, too.