Pence was scheduled to leave Wednesday evening, just hours after Trump minimized the very crisis he sent his aides on an emergency mission to douse. The vice president heads a U.S. delegation that includes Secretary of State Mike Pompeo and national security adviser Robert O'Brien.

"If Turkey goes onto Syria, that's between Turkey and Syria, it's not between Turkey and the United States," Trump said during an Oval Office meeting with Italian President Sergio Mattarella.

As he seeks to push Turkish President Recep Tayyip Erdogan to agree to a cease-fire, Pence will confront doubts about American credibility and his own, as an emissary of an inconsistent president.

A vice president's ability "to have an impact on foreign policy stems from his relationship with the president and his ability to speak credibly for the president," said Jeffrey Prescott, the Obama administration's senior director for Iran, Iraq, Syria and the Gulf states on the National Security Council and a former deputy national security adviser to former Vice President Joe Biden.

"Given how erratic president Trump's decision-making process and style has been, it's just hard to imagine any country on the receiving end of another interlocutor really being confident that what Pence and Pompeo are delivering reflects Trump's thinking at the moment or what it will be in the future," Prescott said.

For Pompeo, the diplomatic mission continues on Friday with two more stops. In Jerusalem, he will meet with Israeli Prime Minister Benjamin Netanyahu to discuss developments in Syria and behavior by Iran, the State Department said. He will fly to Brussels to meet with NATO Secretary General Jens Stoltenberg to discuss transatlantic security issues and U.S. goals for the upcoming meeting of NATO leaders.

Trump's withdrawal effectively abandoned Kurdish forces once allied with the U.S. in the fight against the Islamic State.

The trip comes at a perhaps the darkest moment for the modern U.S.-Turkey relationship and a time of trial for Trump and his Republican Party allies. Trump's failure to deter Erdogan's assault on the Kurds, and his subsequent embrace of Turkish talking points about the former U.S. allies, sparked bipartisan outrage and calls for swift punishment for the NATO ally.

Even as he advertised the Pence trip to protect the Kurds, Trump suggested Wednesday that a Kurdish group was a greater terror threat than the Islamic State, and he welcomed the efforts of Russia and the Assad government to fill the void left by the U.S.

Senate Majority Leader Mitch McConnell called the U.S. relationship with the Kurds "a great alliance."

"I'm sorry that we are where we are. I hope the Vice President and the secretary of state can somehow repair the damage," McConnell said Wednesday.

A former Pence adviser noted that Trump has tasked Pence with sensitive diplomatic missions before, including ratcheting up pressure on North Korea around the Winter Olympics last year, which helped pave the way for talks between Trump and Kim Jong Un.

The White House said Pence will meet Thursday with Erdogan to deliver the message that the U.S. will "maintain punishing economic sanctions on Turkey until a resolution is reached."

But Erdogan has publicly stated that he will be undeterred by the sanctions and resisted calls for a cease-fire Wednesday, saying the fighting would end only if Kurdish fighters abandoned their weapons and retreated from positions near the Turkish border.

But even if Pence can convince Turkey to agree to a cease-fire, which will almost certainly require more leverage than the economic sanctions imposed Monday on Turkey, experts warn it will not erase the signal Trump's action sent to American allies across the globe or the opening already exploited by Russia in the region.

"Deterring an action that hasn't yet been taken is almost always easier than trying to coerce someone to reverse an action that they've already committed blood, treasure and honor to," said John Hannah, former national security adviser for former Vice President Dick Cheney and a senior counselor for Foundation for Defense of Democracies.

As Trump's comments about the crisis drew condemnation on Capitol Hill, two senior administration officials raised alarm that the hastily organized trip lacked achievable goals, with one calling it 'half-baked' and undermined by Trump even before it began. The officials spoke on the condition of anonymity to discuss internal thinking.

Aykan Erdemir, a former member of the Turkish Parliament and a senior fellow at FDD, said that Pence may succeed with Erdogan where Trump failed because he is viewed as a "tough negotiator" in contrast to Trump, who has placed value on international "friendships" with leaders with authoritarian tendencies.

"Erdogan only respects and responds favorably to leaders who he believes are not pushovers," he said, noting that Pence is viewed in Turkey as the chief U.S. advocate for the economic sanctions that led Erdogan to free American pastor Andrew Brunson in 2018.

Erdogan faces global condemnation for the invasion but also sees renewed nationalistic fervor at home, and any pathway to de-escalation, Erdemir said, would likely need to delicately avoid embarrassing Erdogan at home.

Pence, he added, is "more about action than talk, and in that way he's a good match for Erdogan in these conditions."