WASHINGTON – While Colorado Republicans search for a challenger for Michael Bennet, the Democratic senator continues to pile up campaign cash — nearly $2 million in the second quarter.

Bennet had $4.3 million in his campaign account at the end of June, according to campaign finance reports recently made public.

Since Republican Rep. Mike Coffman of Aurora announced last month that he would not enter the race, state GOP leaders have been searching for a candidate they think could defeat Bennet.

From April through June, Bennet took in $1.4 million in contributions from individuals, and $514,900 in donations from special interest political action committees. The PACs represent a variety of financial, health care and other business interests.

While Bennet’s 2016 re-election campaign raised a lot during the quarter, it also spent more than $500,000.

The campaign paid three fundraising firms — Golden State Strategies of Santa Monica, Calif.; HM Consulting of Washington, D.C.; and Straus Baker LLC of New York— a total of nearly $100,000 during the first quarter.

Bennet had debts of about $400,000, according to the report, most of that from loans he made on his 2010 campaign.

Three Republicans have filed as candidates for the seat with the Federal Election Commission: Charles Ehler, Fountain; and Michael Kinlaw and and Darryl Glenn, both of Colorado Springs.

Glenn reported raising $12,375 in the first quarter and began the second quarter with $8,851. His second-quarter report was not yet public. No fundraising reports were available for the other two potential candidates.

Bennet raised $11.5 million when he was elected to his first full term in 2010, defeating Republican Ken Buck.

Republican Sen. Cory Gardner raised $12.3 million when he defeated Democratic incumbent Mark Udall in 2014. Udall raised $20.6 million. The candidates’ spending was dwarfed by the $70.4 million spent by outside groups in the race.