WASHINGTON — A conservative group backed by powerful GOP donors Charles and David Koch is taking to task a prominent Texas Republican as part of a national campaign that chides lawmakers for recently passing a $1.3 trillion spending bill.

Americans for Prosperity said on Friday that Round Rock Rep. John Carter will be subject to mailers and other ads in the coming days over concerns about "wasteful government spending."

"Washington does not have a revenue problem, it has a spending problem," said Jerome Greener, AFP's state director in Texas. "Regrettably, Judge Carter has been part of that problem. We believe it is high time for him to start being a part of the solution."

The campaign will also hit Rep. Beto O'Rourke, an El Paso Democrat now running for U.S. Senate, and Rep. Henry Cuellar, D-Laredo.

But Americans for Prosperity's attention to Carter stands out, given the Republican's senior role on the House Appropriations Committee. It also raises the prospect that the group in the coming months might target other Texas Republicans, including those with tough re-election bids.

Carter on Friday defended his support of the spending bill by pointing to the substantial dollars the legislation provided to the U.S. military.

"I vote for the people of TX-31," he said in an emailed statement, referring to his Central Texas district. "My district has the highest population of veterans in Texas and is home to the largest active-duty military installation in the free world, Fort Hood.

"The FY18 funding bill made major investments in rebuilding our military and investing in veterans care, and I will never vote against our soldiers, veterans and their families."

The $1.3 trillion spending bill approved by Congress in March has proved to be a sore spot for the GOP, particularly as the federal deficit has ballooned since President Donald Trump took office.

Eighteen Republicans were among the 23 Texans who backed the far-reaching legislation. The package resulted from weeks of high-stakes negotiations between Republicans and Democrats as lawmakers sought to avoid yet another government shutdown.

Officials in both parties have offered varying reasons for backing the legislation.

Many Republicans, while grumbling about the bill's largesse, have explained their vote by pointing to the military. Cuellar, who didn't immediately respond to a request for comment, pointed in March to some specific elements that would benefit those who live in his district.

O'Rourke took to Twitter in March to explain his vote.

"Far from perfect," he said. "But includes a lot of good things for Texas and the country: the biggest pay raise for service members in years, a $7 billion funding increase for veterans, significant funding increases for our schools, and more."

Just voted yes on the omnibus. Far from perfect, but includes a lot of good things for Texas and the country: the biggest pay raise for service members in years, a $7 billion funding increase for veterans, significant funding increases for our schools, and more. (1/3) — Rep. Beto O'Rourke (@RepBetoORourke) March 22, 2018

The Democrat — now challenging Sen. Ted Cruz, who voted against the bill — on Friday dismissed AFP's effort.

"Our grassroots campaign can overcome the Koch network, the PACs, the special interests and the corporations who have captured, corroded and corrupted Congress for far too long," said O'Rourke, who sent a fundraising email about the ads later on Thursday.

Americans for Prosperity doesn't appear likely to back down any time soon. The group is planning to spend hundreds of thousands of dollars across the U.S. on digital, print, radio and mail advertisements that call out lawmakers who backed the spending bill, an official said.

[Listen to AFP's radio against Rep. Beto O'Rourke by clicking here.]

It's unclear whether the effort will eventually go after the most vulnerable Texas Republicans who supported the legislation. That bunch could include Reps. Pete Sessions of Dallas, John Culberson of Houston and Will Hurd of San Antonio.

AFP spokesman Joe Sangiorgio said only that the ads are "just the first wave of AFP's 'Stop Overspending' campaign."

"Our activists will be closely monitoring how members of the Texas delegation vote on spending bills in the coming weeks and months," he said.