From The Atlantic:

And what if the Senate does not convict Trump? The fifth benefit of impeachment is that, even when it fails to remove a president, it severely damages his political prospects. Johnson, abandoned by Republicans and rejected by Democrats, did not run for a second term. Nixon resigned, and Gerald Ford, his successor, lost his bid for reelection. Clinton weathered the process and finished out his second term, but despite his personal popularity, he left an electorate hungering for change. “Many, including Al Gore, think that the impeachment cost Gore the election,” Paul Rosenzweig, a former senior member of Independent Counsel Kenneth Starr’s team, told me. “So it has consequences and resonates outside the narrow four corners of impeachment.” If Congress were to impeach Trump, whatever short-term surge he might enjoy as supporters rallied to his defense, his long-term political fate would likely be sealed.