ADDIS ABABA, Ethiopia — President Obama unleashed a blistering and belittling rebuke of Republican White House hopefuls Monday, calling their attack on his landmark nuclear deal with Iran “ridiculous if it weren’t so sad.”

Standing before television cameras during a trip to Africa, Obama suggested the bellicose rhetoric from some Republican candidates was an attempt to divert attention from Donald Trump, the wealthy businessman-turned presidential contender whose popularity is confounding the Republican field.

“Maybe it gets attention and maybe this is just an effort to push Mr. Trump out of the headlines, but it’s not the kind of leadership that is needed for America right now,” Obama said during a news conference in Ethiopia.

Obama’s comments marked his most direct engagement in the race to succeed him. Until now, he’s largely limited his commentary to policy differences with Republicans, often sidestepping the names of specific candidates.

But the president’s unsparing criticism Monday – targeting candidates Mike Huckabee and Ted Cruz, as well as Trump – underscored his sensitivity to efforts to scuttle the Iran accord, which he hopes will be his signature foreign policy initiative. It also raised the prospect of an aggressive role for Obama in the 2016 presidential campaign.

“In 18 months, I’m turning over the keys,” Obama said. “I want to make sure I’m turning over the keys to somebody who is serious about the serious problems that the country faces and the world faces.”

The president was asked specifically about Huckabee’s assertion that Obama had agreed to a nuclear deal that would “take the Israelis and basically march them to the door of the oven,” a reference to crematoria in Nazi concentration camps during the Holocaust. The Israeli government staunchly opposes the agreement and views an Iranian nuclear program as a threat to its existence.

Obama said the comments from Huckabee, a former Arkansas governor, were part of a broader pattern from Republicans. He also singled out Cruz, the Texas senator, for saying the nuclear deal makes Obama – not Iran – the leading state sponsor of terrorism.

“These are leaders in the Republican Party,” Obama said, seeming incredulous. He suggested the Republican party was breaking longstanding American tradition of not playing “fast and loose” with facts during serious foreign policy debates.

Hillary Clinton, the front-runner for the Democratic nomination, said she was “offended personally” by Huckabee’s comments. His remarks should be “repudiated by every person of good faith,” she said during a campaign stop in Iowa Monday.

Huckabee dismissed the criticism, arguing that what was “ridiculous and sad” was that Obama wasn’t taking Iran’s threats to destroy Israel seriously.

“I will stand with our ally Israel to prevent the terrorists in Tehran from achieving their own stated goal of another Holocaust,” Huckabee said in a statement.

While Huckabee’s comments were aimed at Obama, some members of the Republican field – Trump most notably – haven’t held back in their criticism of each other as next week’s initial Republican debate draws near. Former Florida Gov. Jeb Bush called on his colleagues Tuesday to tone it down.

“We have to campaign with joy in our hearts – not anger,” Bush said during an event outside Orlando. “We shouldn’t say outrageous things that turn people off to the conservative message. Our message is the one of hope and opportunity for everyone.”