Similarly, the Affordable Care Act, one of the most far-reaching and beneficial laws to have been passed by Congress in years, gets little respect even among the Democratic candidates who voted for it. Though none support the Republican position of repeal, most talk about the need to “fix” the health law, as if it were a wreck alongside the road rather than a vehicle providing millions of people with health coverage.

“When I think about the health care law, frustrated, disappointed, you can put a lot of words toward it, but every day I work to try to fix it,” said Senator Mark Begich of Alaska, in a radio ad. (Mr. Begich voted for the law.) In a recent debate, Senator Kay Hagan, a Democrat of North Carolina, talked mostly about the “common-sense fixes” she wants to make to the law.

Several Democratic candidates, including Ms. Hagan, Ms. Nunn, and Senator Mark Pryor of Arkansas, quickly adopted the right-wing talking point that President Obama needs to impose a travel ban on all residents of African countries with Ebola cases, even though most public-health experts say such a ban would be ineffective and could make the situation worse.

Senator Mary Landrieu of Louisiana, who has fought loudly against the president’s energy policies, has scurried so far to the right that she even opposes legalizing marijuana for medical purposes, though her leading Republican opponent supports it.

Many of these candidates are running in difficult political environments and are being careful about what they say or don’t say in hopes of preserving Democratic control of the Senate. They run the risk, though, of alienating important constituencies who prefer a party with a spine, especially black voters, who remain very supportive of Mr. Obama. By not standing firmly for their own policies, Democrats send a message to voters that the unending Republican criticism of the president is legitimate. There is much that is going right in this country, and there is still time for Democrats to say so.