South Carolina Rep. Mark Sanford salvaged his political career after an embarrassing sex scandal, but he may have to pull out another impressive save Tuesday as he faces down a surprisingly competitive GOP primary.

Sanford, the former governor of South Carolina who faced national ridicule when he claimed to be “hiking the Appalachian Trail” after a disappearance related to an extramarital affair, returned to politics in the state’s First Congressional District in 2012. He faced a formidable primary challenge in 2014 but managed to win without much campaign spending.

But in his race now against state Rep. Katie Arrington, Sanford is opening his wallet for a last minute ad buy — a sure sign of worry about the close contest. And the reason for the Republican-on-Republican conflict in this reliably GOP district? It's all about Donald Trump. 

Ad-buying tracker Advertising Analytics now reports that Sanford has placed almost $350k on the airwaves in recent weeks, compared to about $280k for Arrington.

Sanford’s recent ads push back at Arrington’s criticism that the former governor hasn’t been sufficiently loyal to the president. (Sanford has, for example, called the president’s steel and aluminum tariffs “an experiment with stupidity,” and he has suggested that Trump’s rhetoric has been divisive and bad for the country. ) In a recent ad, Arrington suggests that “it’s time for a conservative who will work with President Trump, not against him.”

In one of his TV commercials, Sanford tells viewers, "Overwhelmingly, I've voted with the president, and a long list of independent scorekeepers will tell you so."

In another ad, he's voiced support for Trump’s signature immigration proposal, saying "I've supported efforts to secure the border and build a wall."

Meanwhile, Arrington also hasn't been shy about reminding voters of the scandal that nearly toppled Sanford's career. "Mark Sanford and the career politicians cheated on us," she says in another ad. "Bless his heart, but it's time for Mark Sanford to take a hike. For real this time."