This pair of file photos shows incumbent U.S. Sen. Susan Collins, R-Maine, in 2019, left, and Maine House Speaker and Senate contender Sara Gideon, D-Freeport, right. Credit: AP

House Speaker Sara Gideon, the frontrunner in an upcoming Democratic primary to challenge U.S. Sen. Susan Collins, raised $8.1 million during the pre-primary period, extending her fundraising lead over the incumbent Republican.

Updated fundraising reports were due to the federal government on Thursday covering the period from April 1 through June 24. Gideon’s fundraising surge put her over $23 million in total money raised. She spent $7.2 million in the period, leaving her with $5.5 million in cash on hand. It is the first time she has been left with more cash than Collins after a fundraising period.

Collins raised $3 million while spending $3.6 million, according to federal filings. That brings her total fundraising this cycle to $16.2 million. Her campaign had $5 million in cash on hand at the end of the period.

The U.S. Senate race is already the most expensive in Maine’s history. Gideon’s total raised for the period exceeds the $8 million spent by Collins during her 2008 race against then-U.S. Rep. Tom Allen. She won easily in what was previously the priciest campaign in state history.

In addition to spending by Collins and Gideon, outside groups on both sides have also invested heavily in the race, which is considered by both parties to be a pivotal seat in the fight to control the Senate, where Democrats need to pick up at least three seats for a majority.

Independent expenditures from party-affiliated committees as well as several other super PACs total $13.2 million so far, plus millions more from dark-money groups affecting the race. The majority of independent expenditure spending has been negative, according to federal data.

All of that spending comes before the July 14 primary, where Gideon is facing lobbyist Betsy Sweet and Saco lawyer Bre Kidman. Sweet has the backing of several progressive groups and has raised nearly $650,000 this cycle while Kidman has made a point of abandoning fundraising to help with coronavirus relief, saying candidates should adopt a different political model.

Independent candidates Lisa Savage, a former Green party candidate, and Max Linn, a pro-Trump conservative, have also submitted signatures to make the general election ballot, which will be finalized later this summer.