The Democrats should be wary of the Jeremy Corbyn/Labour Party effect: A Socialist-focused agenda and failure to confront Anti-Semitism in the party is a losing strategy.
Another problem Democratic candidates face is the impeachment process. Impeachment has become a partisan political brawl. It has not gained support among Republican voters, who are strongly opposed, or among independent voters, who are evenly divided on its appropriateness. Recent Politico/Morning Consult polling shows overall support for impeachment barely breaking the 50 percent range. Further, polls of voters in battleground states revealed impeachment unpopular there.
Without broad-based support, impeachment will backfire on the Democrats. It will hurt their 2020 presidential election prospects. The Republican-controlled Senate will surely acquit. Trump will claim vindication and victory and be in a better position to win the 2020 Electoral College vote.