Only one Democratic senator was still dangling the possibility of voting for Supreme Court nominee Brett M. Kavanaugh on Thursday afternoon: Sen. Joe Manchin III. As he boarded an elevator, the West Virginia Democrat was confronted by a protester.

“As a survivor, I don’t understand how you can’t look me in the eye,” the woman said.

“I can,” Manchin replied. “I’m looking right at you.”

“Why are you going to vote yes on this?” the protester asked.

“How do you know I’m going to?” the senator answered.

The tense exchange captured by ABC News illustrates how the fight over Kavanaugh, who has been accused of sexual misconduct, has put Manchin and other centrist Democrats in a difficult position. Running for reelection in a state President Trump won by 43 points, Manchin is caught between conservative voters demanding Kavanaugh’s confirmation and liberal activists who vigorously oppose it.

As the Senate barrels toward a pivotal Friday vote to advance Kavanaugh’s nomination, the list of fence-sitting Democratic senators has narrowed to just him. The other holdout, Sen. Heidi Heitkamp (N.D.), announced Thursday that she would join the rest of the Democratic caucus in voting against the federal appeals court judge.

Senate challengers in red states also face pressures similar to Manchin’s. In Tennessee, the Democratic Senate nominee remained undeclared, and in Arizona, the nominee announced her opposition to Kavanaugh late Thursday. Their GOP opponents have voiced support for Kavanaugh.

In battleground races, the GOP is airing ads touting Republican support for Kavanaugh and upbraiding Democrats for their resistance — a move they believe will energize core voters just weeks before the election and one that has caused some Democrats to voice concerns behind closed doors.

During a Wednesday morning meeting of Senate Democrats, multiple senators expressed frustration over how Republicans have successfully energized their base in the Kavanaugh battle, according to an official in the room who spoke on the condition of anonymity to describe the discussion.

The late-breaking decisions and wavering by Democrats highlight the immediate political challenges the Kavanaugh standoff has posed to the party, which needs to win races in Trump-friendly states to have any hope of seizing the Senate in November.

No Democrat is feeling the pressure more than Manchin, who is running in a state where Trump has campaigned for Manchin’s GOP opponent, state Attorney General Patrick Morrisey.

In his Thursday exchange with the protester, Manchin emphasized that he still had an open mind.

“How are you not listening to us as survivors?” the woman asked during the exchange.

“No, I am listening to you,” Manchin said.

“Are you? You’re going to get in this elevator? Look, how are you going to vote? Tell me.”

“I can’t tell you now,” Manchin replied. “We’ll have the vote tomorrow.”

Republican officials have long believed that if they can get 50 of the 51 GOP senators needed to clinch Kavanaugh’s confirmation, they have a chance of winning Manchin’s support and putting a bipartisan label on the vote.

Democrats are trying to seize the GOP’s slim 51-to-49 Senate majority in the midterms. They are defending 10 seats in states Trump won, forcing many of their candidates to strike a tricky balance between placating conservative voters and appealing to party loyalists.

Heitkamp, who is seen as the most vulnerable Democratic senator, issued a lengthy statement Thursday explaining her decision on Kavanaugh. She praised Christine Blasey Ford, the California professor who testified that Kavanaugh sexually assaulted her when they were in high school. Kavanaugh has firmly denied her claims.

“When I listened to Dr. Ford testify, I heard the voices of women I have known throughout my life who have similar stories of sexual assault and abuse,” Heitkamp said. She said in an interview with North Dakota’s WDAY-TV that if she were playing politics, she would vote the other way.

The Republican Senate nominee in North Dakota is Rep. Kevin Cramer, a Trump loyalist who has a double-digit lead over Heitkamp in recent polls. Cramer recently questioned whether a sexual assault accusation against Kavanaugh should disqualify him, even if it is true. Heitkamp’s campaign criticized the remark.

Heitkamp’s brother, Joel, a talk-show host in North Dakota and former Democratic state senator, described his sister’s opposition to Kavanaugh as a vote of conscience.

“I don’t think this is about reelection,” Joel Heitkamp said in an interview on MSNBC with anchor Katy Tur. He added: “She may lose. But in the morning, when she’s brushing her teeth, she needs to like the person she sees.”

An NPR/PBS NewsHour/Marist national poll released Wednesday showed the Democratic enthusiasm advantage in the midterms shrinking. Republicans said their private polling also showed encouraging signs, as the Kavanaugh fight has taken center stage.

“We knew they were energized on the left, and I think this is going to have consequences in the midterm elections,” said Senate Majority Whip John Cornyn (R-Tex.).

Sen. Chris Van Hollen (Md.), the chairman of the Democratic Senatorial Campaign Committee, downplayed the Marist survey and said he believed health care is the top issue for voters.

“You’re obviously seeing people engaged in this debate over the Kavanaugh nomination and it’ll be interesting to see how that engagement ebbs and flows,” he said in an interview.

One major test case will be in Indiana, where vulnerable Democratic Sen. Joe Donnelly announced last Friday that he would vote against Kavanaugh. He argued in a six-paragraph statement that he held “deep reservations” about Kavanaugh’s nomination, particularly in the absence of an FBI probe.

He released his statement just before undeclared Republican senators forced GOP leadership and the White House to put off a planned vote so the FBI could investigate the allegations against Kavanaugh. A senior aide said this week that Donnelly’s opposition to Kavanaugh still stands.

In Missouri, another state Trump won, Republican nominee Josh Hawley released a new ad on Wednesday attacking Democratic Sen. Claire McCaskill, who has said she will vote against Kavanaugh. “I will fight for the Supreme Court. It’s the last line of defense for our values,” Hawley says in the ad.

In Tennessee, former governor Phil Bredesen, a centrist Democratic Senate candidate, has not said how he would vote on Kavanaugh. Rep. Kyrsten Sinema, a moderate Democratic Senate candidate in Arizona, said she will oppose his confirmation.

Manchin was one of three Democratic senators who broke ranks to vote for Trump’s previous Supreme Court nominee, Neil M. Gorsuch. The others were Donnelly and Heitkamp.

Manchin said Thursday that he was still looking at the FBI report on the allegations against Kavanaugh. Key Republican swing votes signaled satisfaction with the report, while many Democrats criticized it as rushed and incomplete.

As he weighs his choice, Manchin also faces pressure from an angry liberal base that has forcefully rejected Trump’s nominee, including some colleagues during Senate lunches and votes.

“Search your souls,” Sen. Mazie Hirono (D-Hawaii) advised any Democrat tempted to vote for Kavanaugh. “Do the right thing.”

Gabriel Pogrund and Philip Rucker contributed to this report.