Democrat Sara Gideon concedes to GOP Sen. Susan Collins in Maine

Democrat Sara Gideon has conceded the Maine Senate race to incumbent Republican Sen. Susan Collins, a top target of Democrats.

"We came up short," Gideon told supporters on Wednesday afternoon. She said she'd called Collins to wish her well.

"I congratulated her on winning this election and told her I'll always be available to help serve the people of Maine," Gideon said.

Collins called the call "very gracious." "We had a good talk," she said.

NBC News projected that Collins was the apparent winner of the race, the most expensive in Maine history. Collins raised more than $26.5 million and spent over $23 million, while Gideon brought in more than $68.5 million and spent nearly $48 million, according to the Center for Responsive Politics.

Collins said after the Gideon call, "I feel this is an affirmation of the work I’m doing in Washington, fighting hard for the people of Maine."

Democrats had hoped Gideon would help them flip the Senate, and she had been leading the race in public polling.

“The other side thought they could come to Maine and just run negative ads, dump loads and loads, millions and millions of dollars of money, and just buy the Senate seat,” Collins told supporters Tuesday night. “Is that the Maine way? No, it certainly is not,” she said.

Gideon's campaign manager Amy Mesner had suggested on Tuesday night that they were in it for the long haul. “Over the coming days, we will make sure that every Mainer has their voice heard in this election,” Mesner said.

The seat was a top target for both parties.

The election, in part, functioned as a referendum on Collins — the only GOP senator from New England — who waffled on her support of President Donald Trump, though she backed his agenda in the Senate two-thirds of the time.

As the election neared, Collins appeared to attempt to distance herself from Trump whose policies have proven unpopular in Maine, most notably voicing her opposition to Supreme Court Justice Amy Coney Barrett’s last-minute nomination.

Still, Collins acted as a pivotal vote against Trump’s impeachment, supported his tax cut and approved Justice Brett Kavanaugh during a contentious Senate hearing, earning her the ire of Democrats and some independents.

But while her support of Trump might have helped her hold on to support of the conservative base, it did not ensure the broad political coalition that had kept her in power for more than two decades.

As speaker, Gideon made a name for herself by shepherding through Medicaid expansion and passing legislation that helped combat the opioid crisis, address climate change and tackle poverty within the state. She received praise in the statehouse for working across the aisle — a posture which has also served as a core element of Collins’ own political brand.

Gideon, who has served as Maine’s speaker since 2016, attempted to frame the race as a national referendum on national leadership in Washington, continuously tying Collins back to Senate Majority Leader Mitch McConnell and to Trump.

“Mitch McConnell will continue to be the Senate majority leader as long as Susan Collins is in the Senate, and that means all the issues we care about, whether health care or the judiciary, will continue to be at risk,” Gideon said during a debate last month.