The conservative super-PAC Ending Spending is airing ads accusing Rep. Phil GingreyJohn (Phil) Phillip Gingrey2017's top health care stories, from ObamaCare to opioids Beating the drum on healthcare Former GOP chairman joins K Street MORE (R-Ga.) of being a big spender, the first direct attacks on the congressman of the election cycle.

Gingrey, one of five viable GOP candidates in the race, is one potential nominee establishment Republicans worry about in the competitive race.

It's unclear what Ending Spending's motivations are, however. The group, backed by conservative Ameritrade founder Joe Ricketts, has been a bit unpredictable in who it backs in past campaigns, sometimes supporting establishment candidates and sometimes helping Tea Party favorites. It's also been on the air in Georgia attacking Democrat Michelle Nunn. 

An Ending Spending spokesman didn't respond to a request for comment on why the group was targeting Gingrey.

"You judge Washington politicians by their actions. Congressman Phil Gingrey says he's a conservative. But up north Gingrey requested millions more in spending, earmarks, Obama's cash for clunkers, increased the debt limit by trillions, and complained he's 'stuck' by only taking a $172,000 tax-payer paid salary. Phil Gingrey: Big spender in the House, wrong for the Senate," the ad's narrator says.

Gingrey's campaign is already fundraising off the ad.

"A Chicago-based special interest group launched an advertisement attacking Dr. Phil Gingrey today," says an email sent to supporters. "Their motivation is a clear indication that his establishment opponents see he's moving up in the polls, and is the most viable constitutional conservative in the race for U.S. Senate."