Defense Secretary Pete Hegseth has had a rocky trip to Europe this week.

In his debut on the world stage, Mr. Hegseth told NATO and Ukrainian ministers in Brussels on Wednesday that a return to Ukraine’s pre-2014 borders was “an unrealistic objective” and ruled out NATO membership for Kyiv. A few hours later, President Trump backed him up while announcing a phone call with President Vladimir V. Putin of Russia to begin peace negotiations.

Facing fierce blowback the next day from European allies and President Volodymyr Zelensky of Ukraine, Mr. Hegseth backpedaled, denying that either he or Mr. Trump had sold out Ukraine or taken bargaining chips with Russia off the table. “There is no betrayal there,” Mr. Hegseth said.

That’s not how even Republican supporters of Mr. Hegseth saw it. “He made a rookie mistake in Brussels,” Senator Roger Wicker, a Mississippi Republican who heads the Armed Services Committee, told Politico on the sidelines of the Munich Security Conference, referring to the secretary’s comment on Ukraine’s borders.

“I don’t know who wrote the speech — it is the kind of thing Tucker Carlson could have written, and Carlson is a fool,” said Mr. Wicker, referring to the conservative media personality and former Fox News host.

Mr. Hegseth sought to recover on Friday, saying in Warsaw that his goal had simply been to “introduce realism into the expectations of our NATO allies.” How much territory Ukraine may cede to Russia would be decided in talks between Mr. Trump and the presidents of the warring countries, he said.

In all, it was a bruising, 72-hour crash course in the geopolitical realities of a job that critics complain Mr. Hegseth, a 44-year-old former National Guard infantryman and Fox News host, is unqualified to hold.

Mr. Hegseth’s trip to Europe, his first overseas visit since being sworn in on Jan. 25, started off on an unusual note.

On an Air Force cargo plane flying to Germany, he signed a memo renaming an Army base in North Carolina to Fort Bragg — skirting a 2021 federal law that banned the naming of bases in honor of soldiers who rebelled against the Union during the Civil War. The previous honoree was Braxton Bragg, an incompetent Confederate general. Mr. Hegseth chose to rename the base for an obscure private, Roland L. Bragg, who earned the Silver Star in World War II.

“Bragg is back,” Mr. Hegseth said in a video of himself signing the memo that he quickly posted on social media.

After a few hours of sleep, Mr. Hegseth joined an early-morning workout with Army Green Berets on Tuesday, and posted photos of himself running and lifting weights with them.

At a base in Stuttgart, Germany, that houses the Pentagon’s commands overseeing operations in Europe and Africa, the secretary took his first questions from reporters and offered the main themes for the trip: European countries must boost military spending and weapons production, and the main national security threat facing the United States is the unchecked flow of migrants across its southwestern border.

The next day in Brussels, Mr. Hegseth spoke at the first Ukraine Defense Contact Group meeting of the Trump administration, though not as its leader.

On Feb. 6, the Pentagon announced that Mr. Hegseth had relinquished America’s leadership of the Contact Group — a collection of more than 50 nations that his predecessor formed shortly after Russia’s full-scale invasion of Ukraine to coordinate shipments of military and humanitarian aid to Kyiv.

According to data compiled by The New York Times, the United States has provided approximately $67 billion in military assistance to Kyiv since the February 2022 invasion, roughly half in shipments of weaponry from the Pentagon’s existing stockpile and half in funds to allow Ukraine to buy military hardware directly from the U.S. defense industry.

Mr. Hegseth, sitting three seats from Rustem Umerov, Ukraine’s defense minister, said the idea of Ukraine retaking its land occupied by Russian forces since Moscow’s first invasion in 2014 was “an unrealistic objective” and “an illusionary goal.”

Those remarks, which signaled the White House’s willingness to cede occupied Crimea and Ukraine’s Donbas region to Mr. Putin before cease-fire negotiations even began, stunned officials in Washington, as well in Kyiv and European capitals.

Former Pentagon officials said it was highly unlikely that Mr. Hegseth’s prepared remarks had not been cleared and coordinated with the White House’s National Security Council before delivery, given his relative inexperience and that he was leading off an important foreign policy week for the Trump administration.

The National Security Council and the Pentagon did not respond to emails requesting comment on the matter. When asked by reporters on Friday if he was aware of what Mr. Hegseth was going to say to the Contact Group, Mr. Trump said, “Generally speaking, I was.”

After meeting with NATO defense ministers in Brussels on Thursday, Mr. Hegseth appeared to soften his earlier statements, saying that “simply pointing out realism, like the borders won’t be rolled back to what everybody would like them to be in 2014, is not a concession to Vladimir Putin.”

“It’s a recognition of the hard power realities on the ground,” he added.

But the secretary repeated his call for European allies to increase military spending and ease their reliance on Washington to safeguard the continent’s security. “President Trump will not allow anyone to turn Uncle Sam into Uncle Sucker,” he said.

On Friday, when Mr. Hegseth visited Poland, he appeared to tack yet again, this time closer to his original remarks on Wednesday, seeking to align himself with Mr. Trump and the president’s national security team. He said that a return to Ukraine’s pre-2014 borders was “unlikely” in the peace agreement between Ukraine and Russia that Mr. Trump sought to broker.

Mr. Hegseth also pushed back against concerns that a cease-fire mediated by Mr. Trump would embolden Mr. Putin. “He’s going to declare victory no matter what,” Mr. Hegseth said at a news conference in Poland, which he praised as a “model ally on the continent” for its security spending and military preparedness on Europe’s eastern flank.

Mr. Hegseth also repeated his earlier assessment that U.S. troops were unlikely to serve on the ground in Ukraine as part of any cease-fire buffer force. That contradicted Vice President JD Vance, who told The Wall Street Journal on Friday that the option of sending U.S. troops to Ukraine if Moscow failed to negotiate in good faith remained “on the table.”

Mr. Hegseth insisted there was no daylight between himself and Mr. Vance, and that the entire Trump national security team was “on the same page.” And his back-and-forth stances were not visible in a video compilation of trip highlights that the Pentagon posted on X Saturday morning.

Outside the halls of NATO headquarters and American military commands, Mr. Hegseth and his wife, Jennifer Rauchet Hegseth, also had an uneven experience.

At a Defense Department middle school in Stuttgart, Germany, students walked out in protest when the Hegseths visited earlier in the week, Jessica Tackaberry, the communications director for the department’s education system in Europe, confirmed.

Over the past two weeks, the Defense Department’s education system in Europe has been vetting its instructional materials and libraries to comply with Mr. Trump’s recent executive orders focused on stamping out diversity, equity and inclusion initiatives from schools, federal programs and the military.

Of all of Mr. Trump’s cabinet secretaries, Mr. Hegseth has been among the most enthusiastic enforcers of those orders.