Sen. Lindsey Graham (R) is touting his conservative record on foreign policy in a six-figure ad buy in South Carolina.
Graham's campaign on Monday said the buy, featuring radio and TV ads, began last week during the college basketball conference tournaments.
Graham is facing a crowded GOP primary in his effort to win a third term this year.
"In a dangerous world, where the only guarantee of peace is strength, Lindsey Graham stands strong," the narrator says in the 30-second TV ad, spliced with clips of Graham asserting he would not stop criticizing the president.
Graham is "a conservative leader who gets things done" the narrator goes on.
The one-minute radio ad highlights endorsements from former President George W. Bush and other veterans groups. It also touts his support for Israel.
"He is standing up to Barack Obama's failed foreign policy and standing with America's longtime ally Israel," another narrator says.
The ad is spliced with clips of Graham's past comments linking the Obama administration's failure to hold anyone accountable for the 2012 terrorist attack on a diplomatic mission in Benghazi, Libya, and Russia's action in Crimea.
Graham has taken a hard line against the president, saying his lack of leadership in other parts of the world has emboldened Russian President Vladimir Putin's recent invasion into the Crimean Peninsula.
Graham is one of a handful of Republican senators who has backed a Senate proposal authorizing $1 billion in loan guarantees to Ukraine. The bill would also authorize sanctions and International Monetary Fund reforms other Republicans have resisted. He was caught on a live microphone last week offering assistance to Secretary of State John Kerry to help persuade House Speaker John Boehner (R) to reach a deal.
Graham is facing off against five other Republicans in the June primary. If he does not reach 50 percent, he will face a runoff two weeks later. A poll released last month showed him pulling in 45 percent of the vote. Since then, another GOP candidate has entered the race.