Perhaps most pointedly, she suggested that Gideon is from away — a serious charge in a state that can turn its nose up at outsiders.

“I grew up in Caribou, I’ve lived in Bangor for 26 years. My family’s been in Maine for generations. She’s been in Maine for about 15 years and lives in Freeport,” Collins said acidly of Gideon, who was born and raised in Rhode Island. “That's a big difference in our knowledge of the state.”

The fusillade of charges comes in response to a barrage of anti-Collins ads that portray her as in the pocket of big business, timid in the face of President Donald Trump and worst of all, losing the support of the state’s famously independent voters. The race has featured nearly $90 million in TV ads and will see another $25 million or more over the home stretch, according to an analysis of media buys, making it easily the most expensive race in Maine history.

Collins’ 24 years in the Senate, where she carefully cultivated the image of a pragmatic centrist, is now in serious danger of being washed away under a flood of ads and rising anti-Trump fervor. And if she goes down, the Senate Republican majority may go with her.

Collins has not led a public poll since July and is increasingly viewed by handicappers as an underdog after crushing her competition in her last three election campaigns. Poll averages show Gideon leading by 6 points, though a Bangor Daily News poll on Tuesday showed her trailing by just one point. The state uses ranked-choice voting, adding to the complexities in the race.

Collins would not concede anything, only offering that the race is “essentially tied.”

“It’s very frustrating because it’s backed by so much money. And it's been going on for two years now: Non-stop negative ads. That eventually it pulls you down,” Collins said of the campaign against her. “What's amazing is that I’m still going to win.”

Gideon’s campaign declined to respond to Collins in an interview, asserting her schedule was too packed. Typically, challengers to high-profile senators will do any media they can get to boost their message, but Gideon seems happy not to make waves.

“Senator Collins’ votes for 181 of Trump’s far-right judicial nominees, for the corporate tax giveaway that put Mainers’ health care in jeopardy and her continued refusal to stand up to Mitch McConnell and Donald Trump show just how much she's changed after 24 years in Washington,” said Maeve Coyle, a Gideon spokeswoman, in a statement. “Her desperate, misleading attacks on Sara make clear that she’s willing to do anything to stay there.”

Collins built her brand to withstand the political winds no matter which way they blew, with a focus on deal-cutting, accessibility and delivering for her state. She will be the Senate Appropriations chairman if her party can keep the Senate. And Collins almost surely must win for there to be any hoping of preventing a Democratic takeover.

Republicans describe Collins as wounded but still in it. Sen. John Kennedy (R-La.) said Democrats have “have hit Susan so hard they’re working now on scar tissue.”

“She can survive the onslaught. But it’s a challenge,” said Sen. Rob Portman (R-Ohio), an ally.

Collins’ precarious position reflects how it’s become borderline impossible to carry on as a middle-of-the-road Republican in the Trump era. Her appeals to the dwindling center incite mockery on the left, particularly when she gently chides the president. On the right, conservatives are upset about her opposition to filling the vacant Supreme Court seat, though former Gov. Paul LePage (R), never a robust Collins fan, said people should still “pinch your nose and vote for her.”

Collins had been pushing hard for another relief package to combat the coronavirus and deliver aid to millions of jobless Americans, but Trump killed negotiations with Speaker Nancy Pelosi in a tweet Tuesday — a “huge mistake,” Collins said. From immigration reform to background checks on gun sales, it was just the latest example of Trump and Collins working at cross purposes.

“Bipartisan work has become harder. I don’t think this president has helped make things any easier,” said Sen. Lisa Murkowski (R-Alaska).

Murkowski herself is “struggling” with whether to support Trump and said she would be “very lonely” if Collins lost. The two make up the sum of moderate Republicans currently serving in the Senate.

A significant factor in Collins’ race is also the one she is most reluctant to address: Trump’s reelection campaign. She refuses to reveal whether she will vote for Trump — a tactic that vulnerable Sen. Pat Toomey (R-Pa.) used successfully four years ago, albeit when Trump wasn’t yet president.

Collins did not support Trump in 2016. But she dismissed the issue in an interview, saying that “nobody” asked her about it on a recent swing through the state.

“I wish the president would not tweet insults. There’s a lot about his style that is completely opposite of mine. But that doesn’t mean that he isn’t right on some issues,” she said, listing his aggressive trade policies toward China and his focus on tax cuts.

“My personal presidential preference, I do not believe is an important factor in this race. I’m not saying that the left is not trying to tie me to Donald Trump … they clearly are,” Collins said. But with her votes to save the Affordable Care Act and against some of Trump’s more controversial nominees like Education Secretary Betsy DeVos, “my independence is the same as it’s always been.”

Betsy Sweet, who ran against Gideon in the Senate Democratic primary from the left, said both candidates are running “incessant” attack ads and talking “very little about what they are for.”

Gideon’s “ahead, and I think there definitely is caution there in terms of talking to people and being involved in public debates,” Sweet said of the campaign. “There’s a little bit of: ‘Let’s keep our head down.’”

That’s not a luxury Collins has as she fights her own party on a Supreme Court vacancy and pushes for a deal on a new coronavirus package. And every time Trump finds himself mired in controversy, she’s asked to opine.

Stuck in Washington last week when she was supposed to be touring Maine, Collins wants to make the race a side-by-side comparison between a four-term senator and a statehouse speaker. She said Gideon is “not doing her job in Maine” as speaker by adjourning the legislature and not doing more to address the pandemic, though Democrats say the blame lies with state Republicans for declining to participate in reconvening.

And she suggested Gideon has explaining to do on Dillon Bates, a former state legislator accused of having sexual relationships with students as a teacher. Senate Republicans’ campaign arm launched an ad Tuesday accusing Gideon of a “cover up.”

“Sara’s own spokesperson conceded that Sara had known about this for a long time. And actually said that Sara told Dillon Bates that, should [the scandal] become public, he would have to go. Now, why, whether or not it became public would be the triggering event, and why she didn’t ask for an investigation, are legitimate issues,” Collins said.

Gideon had been aware of the rumors before they became public and was the first legislator to call on Bates to resign, but did not call for an investigation, according to local news outlet WCSH.

In their last debate, Gideon accused Collins of pushing the courts “far to the right” by supporting most of Trump’s judges. And Collins' vote to confirm Brett Kavanaugh to the Supreme Court provided a huge jolt in the push to defeat her. Now Collins finds herself standing with Murkowski against the efforts of 51 GOP colleagues trying to fill the vacancy filled by the late Ruth Bader Ginsburg.

Collins keeps a photo of her and other female senators alongside Ginsburg and former Justice Sandra Day O’Connor in her Senate hideaway. Collins quickly came out against filling Ginsburg’s Supreme Court seat before election, but her position was ignored by Senate Majority Leader Mitch McConnell, who is moving quickly to confirm Amy Coney Barrett.

The episode shows Collins’ willingness to break with her party — and the limits of a lonely moderate’s influence in an increasingly conservative GOP.

“I was saddened by [Ginsburg’s] death to start with. And disappointed that there was a rush to fill the vacancy,” Collins said. “Confirming conservative [and] moderate to conservative judges is Mitch McConnell’s top priority. So, our goals are very different.”

John Bresnahan and Marianne LeVine contributed to this report.