Embattled Democrats Express New Hope With Harris at Top of Ticket

Senator Martin Heinrich, a two-term Democrat from New Mexico, was not on anyone’s watch list of incumbents facing serious re-election trouble given the reliable partisan tilt of his state, which has not voted for a Republican for Senate since 2002 or a Republican presidential candidate since 2004.

But in the weeks after President Biden turned in a disastrous debate performance against Donald J. Trump last month, Mr. Heinrich was among the Democrats privately panicking. Polls showed New Mexico slipping into an expanding universe of potentially winnable states for the former president — foretelling an electoral disaster for Mr. Biden and trouble in the senator’s own re-election race.

So Mr. Biden’s decision last weekend to exit the race took a weight off the shoulders of Mr. Heinrich and other Democratic incumbents, who now describe a sense of hope and momentum overtaking the doom and gloom that had permeated their party since late June.

“It just feels like a completely different world than a week ago,” said Mr. Heinrich, who is facing a challenge from Nella Domenici, the daughter of the state’s last Republican senator, Pete Domenici, a popular figure and household name in New Mexico. “Across the board — engagement, social media, anecdotal — everything feels different. I feel better about the broad momentum.”

Mr. Biden’s withdrawal is still fresh, polling is only beginning to come in and Democrats still face significant challenges in holding their thin Senate majority and gaining control of the House.

But lawmakers who just days ago were bracing for what they feared would be a November wipeout say the ascension of Vice President Kamala Harris to the top of the ticket has stabilized races and given Democrats a fighting chance. Instead of running from awkward questions about Mr. Biden’s age, mental acuity and fitness, Democrats are hoping to benefit from a surge of grass-roots support for Ms. Harris.