U.S. Rep. Dusty Johnson says he's focused on putting South Dakota first in his congressional work as rumblings have begun about a potential primary election.

But Johnson has been recently pushing his track record of supporting the president — an issue that some Republicans in South Dakota have criticized him over.

Johnson has sent out briefing memos to state Republican leaders since taking office on topics such as his trip to the border and his agriculture work. But the most recent briefing memo outlined the dozen issues on which he supports President Donald Trump and clarified that he supports the funds necessary to construct a wall on the U.S. southern border. Johnson isn't a "rubber stamp" for anyone and he wants Trump focus on the country's strengths instead of talking about other people, the memo states.

More:Rep. Dusty Johnson, House votes to block Trump's emergency declaration

"But I have an excellent working relationship with the White House, and my voting record clearly proves that I have been a conservative voice, a defender of the Constitution and a reliable supporter of the President's agenda," the memo states.

Johnson's vote against Trump's emergency declaration to fund the border wall could provide an opening to a primary challenge in a state where Trump received 61 percent of the vote in 2016. But how much of an impact it could have is up in the air as Trump's disapproval rating has increased in South Dakota, according to Morning Consult polls.

Tapio eyes run for Johnson's seat

Former state Sen. Neal Tapio, the former South Dakota director for Trump's presidential campaign, has increasingly sought to put a wedge between Johnson and Trump supporters in the state with lengthy arguments on Facebook questioning Johnson's support of Trump. As recently as Saturday, Tapio alleged on Facebook that Johnson's support of Trump is "only politically motivated."

The constant criticism has fueled speculation that Tapio, who lost to Johnson in the primary election last year, is eyeing a rematch against Johnson in 2020, and Tapio confirmed on Facebook on Monday that he is "actively considering" a run for U.S. House next year. South Dakotans know he would support Trump, and they're thankful for the direction Trump is taking the country, Tapio wrote on Facebook on Monday.

"The people of South Dakota are hardworking, patriotic Americans who love God, their country, our flag, and they overwhelmingly and unconditionally support our President," he wrote.

More:Neal Tapio forms panel to assess cost of immigrants, refugees to state

Johnson told the Argus Leader that he has been and will continue to be "South Dakota first" in his congressional work.

"I am concerned about getting results for South Dakota — like securing the forage date for our ag producers and making progress on welfare reform — not internet rumblings," he said. "I'd put my record up against anybody."