In particular, they worry the party will remain divided until the summer convention and fear a reprise of 2016, when lingering resentment among Sanders’s supporters over the Democratic National Committee’s favoritism toward eventual nominee Hillary Clinton dampened voter turnout in the fall.

“I hear comments all the time that after what’s happened in the first two primaries we only have a 50-50 chance. It’s not looking good,” said a Democratic senator who requested anonymity to talk about the private concerns of colleagues.

One of the biggest surprises to lawmakers is the poor performance of Biden, who has performed well against Trump in hypothetical matchups…

Others red flags are Trump’s resilient approval rating, despite months of an impeachment inquiry followed by a weeks-long trial, and the amount of money his campaign is raising and spending.