Sen. Mark UdallMark Emery UdallSenate GOP rejects Trump’s call to go big on gun legislation Democratic primary could upend bid for Colorado seat Picking 2018 candidates pits McConnell vs. GOP groups MORE’s (D-Colo.) campaign is looking to make Sen. Mitch McConnell (R-Ky.) a liability for his Republican opponent, Rep. Cory GardnerCory Scott GardnerSenate moving ahead with border bill, despite Trump 13 GOP senators ask administration to pause separation of immigrant families Sessions floats federal law that would protect states that decriminalize marijuana MORE (R) in the race.

The campaign is launching a new line of attack, previewed first to The Hill, asking Gardner whether he supports “McConnell’s prideful legacy of grinding Washington to a halt?”

“As we showed earlier this month, understanding Gardner's long history of supporting gridlock "is as simple as looking at his record in Congress, where he consistently aligns himself with his party’s most obstinate members,’” Udall spokesman James Owens writes.

“Would Gardner seek to continue his legacy of gridlock in the U.S. Senate?”

A Udall aide said the campaign is questioning whether Gardner will back McConnell for GOP caucus leader if elected. But they’ll continue to hammer the theme regardless of his answer, in an attempt to paint Gardner as too extreme for Colorado.

They say Gardner was part of the push to defund ObamaCare that led to the government shutdown, and charge he’s “obstructed” immigration reform.

And the McConnell focus offers them a new avenue for attacks. McConnell has polled as one of the nation’s most unpopular senators, and he’s become an issue for Republicans locked in primary fights already this cycle, as he’s unpopular with both the GOP base and more centrist voters.

The charge that McConnell is a "guardian of gridlock" is one that's been lobbed frequently by the senator's Democratic opponent, Kentucky Secretary of State Alison Lundergan Grimes, and it seems Democrats believe it may be potent outside of the Bluegrass State

Though Colorado's a purple state that's gone Democratic the last two presidential cycles, polling has shown Udall to be vulnerable, with Gardner running low single-digits behind him.