The campaign arm of the Senate Republicans on Monday reserved $6.4 million in TV and radio advertising set to start airing this summer in Colorado as the battle for the seat held by U.S. Rep. Cory Gardner shifts into high gear.

It’s part of an initial $33 million ad buy in seven states, the largest in the National Republican Senatorial Committee’s history.

“Up until now Senate Democrat candidates have led a charmed life, but those days are officially done,” NRSC executive director Kevin McLaughlin told Colorado Politics in a statement.

“This historic NRSC investment will expose every Democrat candidates’ fealty to the socialism-loving extremists running their party and lay waste to the fictional, slick, focus-grouped alter egos created for them by Democrat dark money groups. The stakes have never been higher and the contrast has never been more stark. Buckle your chin straps and put in your mouth guards, it’s going to be a wild ride.”

The Colorado advertising is set to kick off July 8, a week after Democrats settle a primary that’s likely to pit former Gov. John Hickenlooper against former state House Speaker Andrew Romanoff.

While the NRSC has spent minimal funds in the last year portraying Colorado’s Democratic Senate candidates – including Romanoff – as wild-eyed socialists, the bulk of the GOP group’s attacks have been aimed at Hickenlooper, the front-runner for the nomination.

Senate Republicans are playing defense this year, with six of the seven states in Monday’s ad buy held by GOP incumbents, but they’re heading into campaign season with a hefty cash advantage over their rivals.

The NRSC had $30.37 million in the bank at the end of the last reporting period, compared to $19.94 million cash on hand reported by its counterpart, the Democratic Senatorial Campaign Committee, which also reported $1.8 million in debt.  

Democrats have to flip four Republican-held seats to win the majority, or three seats if the party takes the White House.

The NRSC said it’s also booking advertising worth $7.3 million in North Carolina, $5.7 million in Arizona, $5.1 million in Maine, $2.8 million in Montana, $2.7 million in Michigan and $2.6 million in Iowa, with start dates ranging from June 1 in Arizona to Sept. 8 in Montana.

The targeted states mostly align with ad reservations made late last month by the parties’ respective Senate super PACs, with the addition of Montana, considered competitive after Democratic Gov. Steve Bullock announced his run for the GOP-held seat, and Michigan, the lone seat held by a Democratic incumbent.

Considered among the most vulnerable senators on the ballot this year, Gardner helmed the NRSC for the 2018 cycle, when Republicans netted two seats to reach their current 53-47 majority.

The NRSC’s initial spending in Colorado this year is more than the $6.4 million the group spent in 2014 to help Gardner unseat Democrat Mark Udall. It’s also the first spending by the group in Colorado since that election, since the NRSC declined to put any money behind GOP nominee Darryl Glenn, who lost a challenge against Democratic U.S. Sen. Michael Bennet in 2016.

The booking covers radio, cable and broadcast TV but doesn’t include what is expected to be substantial spending on digital advertising, a Republican familiar with the NRSC’s plans said. As is typical with early ad reservations, the total amount spent could increase or decrease as the election approaches.