The group has reserved $1.1 million in advertising in North Carolina for April, its political director, Carl Forti, confirmed Monday. The ads, the content of which Forti would not disclose, will air in the pricey Raleigh and Charlotte media markets.
That influx of spending will hit just before Tillis, the Republican frontrunner, faces off May 6 against a field including Greg Brannon, a physician who has been endorsed by Sen. Rand Paul, R-Ky., and Mark Harris, a Baptist pastor who has received support from former Arkansas Gov. Mike Huckabee.
The victor will take on Sen. Kay Hagan, a Democrat, who is among the most vulnerable incumbents running in this election cycle.
American Crossroads has so far run television ads in a handful of Senate races, but its hefty buy in North Carolina will come at a pivotal time for the Republican Senate field in particular.
Tillis has reserved more than $500,000 in network television advertising for April and the first week of May, none of which will air in Raleigh or Charlotte. His campaign has also reserved more than $350,000 in cable television advertising during that span across all media markets, according to numbers provided by a spokesperson.
Although Tillis is the candidate favored by national Republicans, he has faced a competitive primary race, in which he has failed to consistently outperform Brannon and Harris in public polls. In a recent Public Policy Polling survey, Tillis and Brannon each polled at 14 percent.
Tillis has also struggled to accrue a sizable war chest despite frequent fundraisers with GOP luminaries.
On Monday, Senate Minority Leader Mitch McConnell, R-Ky., and other prominent GOP senators hosted a fundraising event on behalf of Tillis at the National Republican Senatorial Committee headquarters in Washington.
Karl Rove, who founded American Crossroads, has also attended fundraising events benefiting Tillis, and Tillis attended an American Crossroads summit in Washington in October.
Now Rove and American Crossroads might be making good on a plan to intervene in Republican primary races to boost candidates they think would be strongest in a general-election matchup. Last year, American Crossroads announced its Conservative Victory Project, focused solely on preventing weak candidates from advancing to the general election.
Democrats, at least, are confident Tillis will win his primary race: Hagan recently told the Associated Press that her campaign is focused narrowly on taking on Tillis and Americans for Prosperity, the pro-Republican outside group that has already spent millions of dollars so far this election cycle attacking Hagan on television.