Impeachment of an American president is a weighty measure that's only been used a handful of times in our history. And on two of those occasions, the judgment of history has come down against the impeachers.
Andrew Johnson was an awful president, but the move by Radical Republicans in Congress to remove him from office reeked from top to bottom of an effort to resolve a policy dispute by ginning up a legal one — passing a law to bar Johnson from firing Cabinet secretaries and them impeaching him for breaking it. Bill Clinton's impeachment, if anything, suffered from the opposite problem. The charges against him, even if you believed them, simply seemed to have too little to do with the duties and responsibilities of his high office. Republicans had hoped a sex scandal would damage Clinton's approval ratings, it didn't really, and then they went berserk.
The exception that proves the rule is Richard Nixon, whose misdeeds were legitimately "high crimes." Nixon also went down at a period in American history when the ideological polarization of the parties was low — some of his staunchest policy allies were conservative Southern Democrats, while some liberal Republicans were sharp critics of his administration. His downfall represents a kind of founding myth of modern American civic culture, complete with a Robert Redford movie that reserves a key heroic role for conservative icon Barry Goldwater.
The question that faces Congress today is whether the Trump case is more like Nixon or closer to Clinton or Johnson. And the answer is that it's a highly Nixonian situation. Donald Trump is charged with misconduct that is serious and directly relevant to his public office but that isn't simply a reiteration of longstanding ideological disagreements in American life.
The impeachment tool is somewhat clumsy and rarely used, in part because of how clumsy it is. It's not so much that presidential misconduct is rare as that replacing the incumbent president of the United States with his hand-picked vice president is rarely a reasonable remedy for anything controversial and significant. But it's ideally suited to the particular moment in which the country now finds itself. Democrats have enormous disagreements with Mike Pence, but those disagreements are fundamentally unrelated to the core of Trump's obstruction of justice, abuse of power, and financial conflicts of interest — for now, at least.