FILE - ME Sara Gideon, Susan Collins

Maine House Speaker Sara Gideon (left) and U.S. Sen. Susan Collins, R-Maine.

(The Center Square) – Spending on the closely watched U.S. Senate contest in Maine topped more than $185 million, making it one of the most expensive races this election cycle.

Republican Sen. Susan Collins won a fifth term in the Nov. 3 elections, edging out Democrat Sara Gideon by 51% to 42%, according to preliminary results. But Collins' hard-fought victory came on the heels of unprecedented spending by campaigns, super PACs and other outside electioneering groups either supporting or opposing her reelection bid.

"It's not the most expensive race this election cycle, but I'd say it's definitely in the top five," said Brendan Quinn, a spokesman for Center for Responsive Politics, a Washington D.C.-based nonpartisan campaign finance watchdog group. "We saw enormous amounts of money being spent by out-of-state groups to try to influence Maine voters."

Democrats and progressive groups targeted Collins and sought to tie her to President Donald Trump over her vote to confirm Supreme Court Justice Brett Kavanaugh and tax cuts that critics say favored the wealthy. The Maine Senate race was also viewed as a crucial battleground in the fight for control of the GOP-led Senate.

Gideon, who serves as Maine's speaker of the House of Representatives, drummed up nearly $70 million and spent about $49 million as of Oct. 14, according to Federal Election Commision filings. By comparison, Collins' had raised about $24 million and spent most of it as of Oct. 14, FEC filings show.

Two independent candidates, Lisa Savage and Max Linn, reported spending about $650,000 combined, according to campaign disclosures.

But the spending by campaigns pales by comparison to the flood of so-called "dark money" shelled out by super PACs on advertisements supporting and opposing each candidate.

Gideon, who outspent Collins 2-1 in the race, benefited from national Democratic fundraising arms, including the Senate Majority PAC, which spent $27.9 million supporting her and opposing Collins, disclosures show. Gideon also got funds from the Democratic Senatorial Campaign Committee, which spent $4.7 million on TV ads supporting her campaign.

Collins also benefited from outside spending by two of the Republican Party’s largest fundraising arms – the National Republican Senatorial Committee and the Senate Leadership Fund -- which dropped about $30 million on race, according to disclosures. Collins also got help from the 1820 PAC, a group founded specifically to support her reelection bid.

To be sure, the expenditures dwarfed the 2018 contest for the 2nd Congressional District, Maine's previously most expensive race, which drew about $24 million in spending.

The final price tag for Maine's Senate race is likely to grow, as the FEC data doesn't include money raised and spent in the final three weeks before the Nov. 3 election.

Super PACs can raise and spend unlimited amounts of money on behalf of candidates, but they cannot legally coordinate expenditures with campaigns they're backing.

On the campaign trail, Collins and Gideon blasted spending by out-of-state groups, with each accusing the other of relying too heavily on shadowy "dark money" groups.

All told, super PACs and outside groups spent more than $112 million on the Maine Senate race, according to the center's analysis.

“Gideon was by far the biggest beneficiary, but it obviously didn’t push her over the top,” Quinn said. "It shows that money can only go so far, particularly if it’s coming from out of state.”