WASHINGTON — Senator Sherrod Brown of Ohio is a relatively accessible fellow, but when asked for an interview on the subject of the schisms in his Democratic Party, his schedule was full. Instead, he sent a statement that the Hillary Clinton-Bernie Sanders presidential primary battle was strengthening the party in contrast with the “divisive” Republican fight.

He’s right about the Republicans. The personal invective and policy splits threaten to tear the party apart and produce an electoral cataclysm in November.

Yet that is obscuring serious problems on the Democratic side: deep divisions on policy and an almost certain nominee, Mrs. Clinton, who if not for Donald J. Trump would be the most unpopular presidential front-runner in recent times.

The differences between Mrs. Clinton and Mr. Sanders are more pronounced than those between Barack Obama and Mrs. Clinton in 2008. Then, there were modest divergences on health care and national security, highlighted by her support five years earlier for George W. Bush’s decision to invade Iraq. Mainly it was a difference of style and persona, a new voice in an environment of change running against a candidate focused on recapturing the salad days of the last Democratic administration.