AUGUSTA, Maine — Independent U.S. Sen. Angus King of Maine will face two lesser-known candidates who won uncontested primaries Tuesday but now face a difficult challenge against a popular incumbent.

Republican State Sen. Eric Brakey was unchallenged in his primary election Tuesday after an opponent, Max Linn, was disqualified by election officials who determined his nomination petition contained fraudulent signatures. Portland Democrat Zak Ringelstein was also unopposed.

King was first elected in 2012 after Republican Sen. Olympia Snowe abruptly abandoned her re-election bid, citing corrosive partisanship in Washington.

King, a former independent governor, said in announcing his formal re-election bid a few weeks ago that he wants to continue his effort to serve as a bridge between the polarized parties. He said there are "tender shoots of bipartisan cooperation" that need to be encouraged.

"This is a time when we need to continue to try to talk to people, to maintain civil discourse, to try to solve problems and to try to sort of calm some of the rhetoric that passes for political discourse in this country," he said during his announcement.

Republican Gov. Paul LePage toyed with the idea of joining the race, but ultimately endorsed Brakey. He said he'll help in any way that he can.

Brakey and Ringelstein will need to close a fundraising cap.

King has about $2.3 million in his re-election coffers, while Brakey has $84,813 and Ringelstein $29,610, according to campaign disclosure reports.