Sen. Lindsey Graham, R-S.C., said he had a “cordial, pleasant” phone call about national security issues with presumptive Republican nominee Donald Trump Wednesday – an apparent contrast with previous well-publicized spats between the former 2016 rivals.

“I had a cordial, pleasant phone conversation with Mr. Trump. I congratulated him on winning the Republican nomination for President,” Graham said in the statement released Thursday. “I know Mr. Trump is reaching out to many people, throughout the party and the country, to solicit their advice and opinions. I believe this is a wise move on his part.”

Graham said the pair had a fifteen-minute discussion “centered on the national security threats facing the United States.” Graham said he offered his view on the fight against ISIS and the Iranian nuclear deal.

Graham did not endorse Trump but said “I will do what I can in the Senate to help the next president. The next president will inherit a mess.”

Trump has been reaching out to top members of the so-called Republican “establishment,” meeting Thursday with House Speaker Paul Ryan and a number of other GOP leaders as part of an effort to unite the party after a divisive and nasty primary process.

Graham, who ran for the Republican nomination but dropped out in December, has been an especially strong critic of Trump.

The South Carolina senator once said choosing between Trump and Texas Sen. Ted Cruz was like choosing to be poisoned or shot. In January he told Fox News that Trump is “the most-unprepared person I’ve ever met to be commander-in-chief.”

As recently as last week, Graham said he could not support Trump. Trump shot back Friday, saying Graham had “zero credibility.”

“As a candidate who did not receive 1 percent in his own state -- compared to my victory at nearly 40 percent with many others in the race -- he has zero credibility,” Trump said in a statement. “He was a poor representative and an embarrassment to the great people of South Carolina.”

Fox News’ Chad Pergram contributed to this report.