Incumbent U.S. Sen. Michael Bennet of Denver, once seen as vulnerable in his bid for re-election, defeated Republican candidate Darryl Glenn, the El Paso county commissioner, by a comfortable margin Tuesday night.

Glenn was winning his home county 147,055 to 89,526, but lost to Bennet in Denver County 139,262 to 39,062, according to returns from the Secretary of State’s Office.

Bennet also took wins in bellwethers Jefferson County, 136,407 to 115,136, and Larimer County, 77,484 to 68,674. The Associated Press called the race at 8:58 p.m., describing the Democrat as coasting.

Bennet took the stage in Denver for a victory speech at about 9:15 p.m.

“We took care of business here in Colorado tonight,” said the normally low-key senator.

He congratulated Glenn. “I look forward to working together on behalf of Colorado,” he said.

Bennet vowed to work with Republicans and Democrats who are elected Tuesday to represent Colorado.

“People across Colorado understand there is something fundamentally wrong with our national politics and how we’re governing our country,” the senator said. “They are right, and it has to change.

“Here in Colorado we reject dysfunction as normal, partisan gridlock is acceptable, that Democrats and Republicans and independents can’t work together.”

Republicans saw Bennet as vulnerable a year ago, but top-name candidates in the party, including U.S. Rep. Mike Coffman of Aurora and Arapahoe County District Attorney George Brauchler, decided not to jump in.

Glenn won a tumultuous five-way primary in June, promising to stay true to his far-right beliefs throughout the general election campaign. Bennet hammered Glenn for the challenger’s remarks during the GOP primary in which he said he would not compromise with Democrats but would instead lead them. Glenn stated emphatically that he was unlikely to work across the aisle.

Bennet has prided himself on his bipartisanship during his six years in the Senate. He was a member of the Gang of Eight senators, four Republican and four Democrat, who passed an comprehensive immigration reform package out of the Senate in 2013 only to see it mired in partisanship in the House.

Bennet was first appointed to the U.S. Senate in 2009 by then Gov. Bill Ritter, when Sen. Ken Salazar was named to President Obama’s Cabinet as secretary of the interior. He beat then-Weld County District Attorney Ken Buck in 2010, 48.1 percent to 46.4.

Buck won a seat in the U.S. House when Republican Cory Gardner chose to run for U.S. Senate against incumbent Democrat Mark Udall in 2014, Gardner won with 48.2 percent of the vote to Udall’s 46.3 percent.

Glenn’s grass-roots campaign struggled to compete, and he only faced Bennet twice in debate. He went after the Democrat for his votes for the Iran nuclear deal and the Affordable Care Act and his support for clean energy regulations that threaten to put the state’s coal miners out of work.

Bennet stressed his work with Gardner on an “all-of-the-above” energy policy, defended the Iran deal and insisted the health care overhaul could be fixed to make premiums affordable. He campaigned on his willingness to work with Republicans in Washington on such issues as funding for Zika virus research.

Glenn called for the repeal of the health care program, an end to the “war on coal” and cuts in entitlement spending. On education and the economy, he argued that states best know how to fund schools and create jobs. He opposed amnesty for immigrants in the country without legal permission.

Bennet’s fundraising prowess provided an early advantage against Glenn, who has never held statewide office and wasn’t backed by the Republican National Senatorial Committee.

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The Associated Press contributed to this report.