It's no secret that I don't like Trump and think he should be resisted. I'm not alone; Trump is unpopular enought that other people have called for Trump to be impeached and removed from office. I'm not the least bit optimistic about this, at least before 2019, and will let Vox explain why in How to impeach a president.
What we can learn from Reconstruction, Watergate, and the Clinton saga.While Trump "rendered himself obnoxious" even before he entered office, I agree that he'd have to lose the support of at least one-third of the Republiicans in the U.S. Senate for him to be removed from office. That ignores that articles of impeachment would not be passed out of the House Judiciary Committee, let alone be passed out of the House of Representatives, so long as Republicans hold a majority and Trump retains the support of most of his party. I would not hold my breath for that changing. That doesn't mean we should despair. In this case, the Borg are wrong; resistance is not futile.
The founding fathers included impeachment in the constitution so that Congress would have a way to remove leaders who had "rendered themselves obnoxious," in the words of Benjamin Franklin. But the way they set up the process, it's nearly impossible to remove a president from office without substantial support from the president's own party. That's what happened during Watergate: some congressional republicans protected Richard Nixon, but others demanded to know the extent of his involvement in a break-in at the headquarters of the Democratic National Committee, and the subsequent cover-up. In the words of then-Senator Howard Baker, a Republican from Tennessee, "What did the President know, and when did he know it?" It was pressure from Republican leaders like Barry Goldwater that made Nixon resign before the House could vote on articles of impeachment-- Goldwater convinced Nixon that too many Republicans were willing to vote to remove him from office, he'd never survive a Senate vote.
The opposite was true during the impeachment proceedings for Bill Clinton. After it became clear he lied during a deposition for a sexual assault suit brought by a former employee, Paula Jones, about his relationship with a different employee, Monica Lewinsky, Republicans in Congress argued the offense was serious enough to be impeachable. Democrats disagreed, and although the House voted to impeach Clinton on a party-line vote, not a single Democratic senator voted to remove him from office. If a President still has the support of a majority of his political party, history suggests the chances for impeaching and removing him from office are slim to none.
While legal scholars, activists, and some Democratic members of Congress have pushed for articles of impeachment against Donald Trump, it seems unlikely at this point that a substantial number of Republicans would break rank in the Senate to create a 2/3 majority in favor of removal from office.