Possible impeachment scenarios in abbreviated and bullet format. Article excerpts taken from Vox.
1) Trump doesn’t get impeached
The House has not yet voted to impeach Trump. The big swing among House moderates was in favor of launching an “impeachment inquiry” not of impeaching Trump per se.
2) Trump could be forced to resign
Richard Nixon is the only president to have been forced from office by scandal rather than death, but he’s not one of the two presidents who’ve been impeached by the US House of Representatives.
Instead, a delegation of Republican members of Congress — including the minority leaders of the House and Senate, plus conservative icon Barry Goldwater — came to the White House and told Nixon his support in Congress had evaporated. The leaders of both the Republican Party as an institution and the conservative movement were looking to safeguard their own long-term interests and not go down with the rapidly sinking Nixon administration. Faced with that reality, Nixon chose to resign.
3) Mitch McConnell could spike the trial
A trial of Donald Trump would take place in a chamber controlled by his GOP allies. If it doesn’t suit their interests to have extended arguments and presentation of evidence, they don’t need to do that. A quick, party-line vote to acquit could be all we get. Given everything we know about Trump-era politics, this seems like one of the most likely scenarios.
4) A rigorous trial leads to a party-line acquittal
One has to assume that if Trump has his Senate caucus solidly behind him, its members will vote to greatly curtail the trial and move forward.
But, in theory, Senate Republicans could decide they want to go through a whole extended trial and then acquit Trump on a party-line vote. If that happens, then legally speaking nothing happens — Trump just stays president. Democrats might fall into infighting, arguing that if the party leadership had taken a different tactical approach (a broad impeachment inquiry rather than a narrowly Ukraine-focused one, for example) the outcome might have been different.
5) Trump is acquitted, despite an anti-Trump majority
Another possibility is that the Ukraine scandal ends up playing out somewhat similarly to the Affordable Care Act repeal where a small number of Republican senators joined forces with Democrats to secure a majority.
You could imagine the GOP’s vulnerable Senate incumbents — Martha McSally (R-AZ), Cory Gardner (R-CO), and Susan Collins (R-ME) — plus occasional Trump critics Sens. Mitt Romney (R-UT) and Ben Sasse (R-NE) force a real trial and ultimately produce a majority vote in favor of conviction.
Except the Constitution requires 67 votes — not 51 — to remove a president, so that would count as an acquittal.
6) The GOP splits, and Trump is removed from office
Under this scenario, Trump still holds on to his true base (the roughly half of GOP primary voters who backed him in 2016) but becomes so unpopular with the public that he suffers mass defections from GOP senators leading to his removal from office.
For obvious reasons, it’s difficult to imagine this happening. The Republican establishment didn’t like Trump and doesn’t like everything he does, but he’s fundamentally delivered for them on all their key priorities.
7) Pence is complicit, and he’s removed too
One reason Watergate ended up working out so badly for Nixon is that, sort of by coincidence, his original vice president had been driven from office by an unrelated scandal. Consequently, at the time of maximum peril for Nixon, the VP was Gerald Ford — a well-regarded Republican who genuinely had nothing to do with the Nixon White House or any of its crimes.
By contrast, Pence — like other modern VPs — is himself a senior member of the Trump administration.
8) The Presidential Succession Act might be unconstitutional
Many scholars believe that the speaker (and the president pro temp of the Senate) as a member of Congress is not an “officer” under the meaning of the Constitution. It might be good for the Supreme Court to offer its view on this before it needs to be litigated in the middle of a huge national crisis, but America’s top court does not offer advisory opinions choosing instead to rule only on actual controversies. So we’ll never find out if the court will strike this provision down until it actually happens. But suffice it to say it might, in which case Secretary of State Mike Pompeo becomes president.
9) President Steve Mnuchin
The problem with the President Pompeo scenario is that he’s implicated in the scandal even more clearly than Pence.
He was on the infamous call with Ukrainian President Volodymyr Zelensky. But he feigned ignorance about it and only later admitted he was on the call after press reports exposed him. He used to be all for congressional oversight of the State Department when he was in the House and now says questions about the administration’s conduct toward the European nation amounts to “bullying.” And instead of standing by the ambassador to Ukraine, he let the president recall her seemingly for personal reasons.
If by some remarkable turn of fortune, Congress decides it needs to purge everyone involved with the scandal then it’s going to need to remove Mike Pompeo.