Removing a US President by impeachment is hard
When people think of ways to protect America from the threat Trump represents, "impeachment" is one of the first things than comes to mind. Unfortunately, as much as I'd like to be able to cheer on every possible strategy for dealing with Trump, removing a US President by impeachment is uniquely difficult to pull off. That doesn't mean we shouldn't think about it how to do it, but in order for an impeachment to have any chance of succeeding, the first step is realizing how difficult it would be.
An awkward note about jargon: American legalese doesn't have a nice word for "remove an elected official from office by impeachment". "Impeachment" is just the indictment by the US House of Representatives—the president isn't actually removed from office unless convicted in the trial in the Senate. I'm sure most people reading this know that, if only because of the Clinton impeachment, but what people may not realize is that you need a full two-thirds of the Senate to vote to convict in order to actually remove a president from office.
To underline just how hard this makes it to remove a president by impeachment, consider Andrew Johnson. When Lincoln was first elected, he had a fellow Republican as his running mate, but when he ran for reelection in the middle of the Civil War, he decided to replace his former running mate with Johnson, a southerner, as a sign of national unity. Unfortunately, when Lincoln was assassinated, this meant an opponent of civil rights for African-Americans was now president.
Republicans in Congress had to pass many important bills, including the Civil Rights Act of 1866, over Johnson's veto. The 14th Amendment was also passed in spite of Johnson's objections. Johnson went on a speaking tour attacking supporters of racial equality as a danger to the country, in which he also happened to mention he was thinking of firing cabinet secretaries who disagreed with him. Congress responded by passing a law, again over Johnson's veto, limiting his ability to do so. Johnson then proceeded to fire his Secretary of Defense, blatantly ignoring the law.
Removing Johnson from office should have been easy. With most former Confederate states not yet having regained their representation in Congress, the Republican majority in Congress was overwhelming. Johnson had broken a law that Congress had passed with the same majority required to remove him from office. Congress had previously passed numerous laws that Johnson opposed, with similar majorities. Yet the Senate failed to convict Johnson by a single vote.
This doesn't mean getting two-thirds of Senators to vote for removal is impossible. It's been suggested that Nixon resigned because his fellow Republicans told him privately that if he didn't, he'd not only be impeached but convicted. But that only happened after Nixon had pissed off Congress repeatedly and his approval rating was in the toilet.
Legally, the case for removing Trump will be easy to make. His refusal to take any real action to resolve his many conflicts of interest will mean there will be a plausible case for impeachment from the moment he takes the oath of office. Russia's hack of the DNC also offers a close parallel for Watergate—if Trump dared obstruct any investigation of the hack, that would create a second very strong case for impeachment.
But the issue of whether Trump can be impeached and removed from office isn't just legal. It's political. Senators in deep red states aren't going to vote for impeachment unless they believe it's politically wise to do so. If you want Congress to remove Trump from office, you need to convince rank-and-file Republicans in places like South Carolina and Kentucky that it's a good idea.
I think the way we get there is to first fight a series of smaller fights on issues where the unacceptability of Trump's behavior should not be a partisan issue. Pass the Presidential Accountability Act. Tell Congress to hold hearings on Trump's conflicts of interest. Tell Congress to hold hearings on Russian hacking during the election. Refuse to confirm dodgy cabinet picks. In other words, get Congress to do everything possible to contain Trump short of impeachment. Do those things for their own sake—but also because the more of them we do, the more impeachment will become politically possible.