A leading Senate Republican campaign committee is putting $1.25 million into the U.S. Senate race in Colorado, where GOP challenger Joe O’Dea trails Democratic U.S. Sen. Michael Bennet in the polls.

The move by the Senate Leadership Fund, a super PAC aligned with Senate Minority Leader Mitch McConnell of Kentucky, comes a week before ballots go out to state voters and nearly three months after McConnell pledged to go “all-in” on O’Dea’s bid.

The committee contributed the funds on Friday to American Policy Fund, O’Dea’s super PAC, which has already spent around $5 million to support the construction company owner, mostly on advertising.

The super PAC is spending heavily to air ads assailing Bennet as a Washington insider and linking the incumbent to President Joe Biden’s agenda.

“We’ve been monitoring Colorado and we like what we see there. We think Michael Bennet is vulnerable,” Steven Law, president of the McConnell super PAC, said in an emailed statement to Colorado Politics.

Added Jack Pandol, the group’s spokesman: “It’s a race we’re keeping an eye on. We continue to be impressed by the race Joe O’Dea is running in Colorado.”

Polls released since late August have shown Bennet with an average lead of about 10 points over O’Dea, though the incumbent has only reached 50% support in one recent survey – a Data For Progress poll conducted Oct. 3-6 that showed Bennet leading O’Dea 50% to 41%, with 3% support for the Libertarian nominee.

According to the election data crunchers at FiveThirtyEight.com, Bennet is favored to win in 92 out of 100 simulated outcomes, with O’Dea prevailing in just eight out of 100.

Up to this point, national Republican spending groups have mostly stayed on the sidelines in the Colorado race, though the National Republican Senatorial Committee spent about $250,000 in early August to air TV ads tying Bennet to President Joe Biden.

National Democrats and outside groups aligned with the party have spent millions to boost Bennet, who is seeking a third full term.

On Friday, the League of Conservation Voters’ super PAC put more than $1.3 million behind TV ads opposing O’Dea. The spending piles on top of more than $5.5 million worth of attack ads aimed at the Republican from Democratic group 53 Peaks and Giffords PAC, a committee that supports gun restrictions.

A group funded by the Democrats’ counterpart to SLF, aligned with Senate Majority Leader Chuck Schumer of New York, spent more than $5 million earlier this year in an unsuccessful attempt to steer voters toward O’Dea’s more conservative primary rival.

The McConnell super PAC is spending considerably more in other states with competitive Senate races, including in Georgia, Pennsylvania and New Hampshire, with total spending topping $120 million for the cycle, according to the Center for Responsive Politics.