A prominent critic of President-elect Donald Trump appears to be preparing to oppose key aspects of the incoming administration’s foreign policy agenda despite the electoral mandate of America First.

Sen. Mitch McConnell (R-Ky.) is challenging Trump’s foreign policy outlook, urging the president-elect to reject what he describes as America First’s “flirtation with isolation and decline” in an essay published in Foreign Affairs on Monday.

The former Senate Republican leader is also encouraging the administration to adopt many foreign policy positions that Trump notably opposed during the campaign, including supporting increased foreign aid, free trade agreements, solidarity with NATO, and more weapons transfers to Ukraine.

“The [Trump] administration will face calls from within the Republican Party to give up on American primacy,” McConnell wrote in Foreign Affairs. “It must reject them. To pretend that the United States can focus on just one threat at a time, that its credibility is divisible, or that it can afford to shrug off faraway chaos as irrelevant is to ignore its global interests and its adversaries’ global designs. America will not be made great again by those who simply want to manage its decline.”

“The response to four years of weakness must not be four years of isolation,” McConnell wrote.

McConnell’s remarks, which advocate for an interventionist foreign policy similar to the George W. Bush administration and a larger defense budget to deter multiple adversaries, raise questions about how far the Kentucky Republican is willing to go in opposing the president-elect’s nominees and agenda.

“We’re in a very, very dangerous world right now, reminiscent of before World War Two,” McConnell told the Financial Times in an interview published last week. “Even the slogan is the same. ‘America First.’ That was what they said in the ’30s.”

The former Senate Republican leader seems to be most at odds with Trump over the Ukraine issue. McConnell argues that the Trump administration’s strategy for deterring Chinese aggression cannot succeed without preventing a Russian victory in Ukraine.

“Standing up to China will require Trump to reject the myopic advice that he prioritize that challenge by abandoning Ukraine,” McConnell wrote in Foreign Affairs. “A Russian victory would not only damage the United States’ interest in European security and increase U.S. military requirements in Europe; it would also compound the threats from China, Iran, and North Korea.”

Trump has pledged to end the Russia-Ukraine war and has criticized President Joe Biden for escalating tensions with Russian President Vladimir Putin during the final months of his presidency. On the campaign trail, Trump vowed to end the war before he took office, but that was before Biden authorized striking Russian soil with U.S.-made and supplied weapons and other acts of escalation.

Trump said during a press conference on Monday that the conflict was very complicated, remarks that came after he met with Ukrainian President Vladimir Zelenskyy in Paris earlier this month.

“It’s crazy what’s taking place. It’s crazy. I disagree very vehemently with sending missiles hundreds of miles into Russia,” Trump told TIME during his 2024 Person of the Year interview on Thursday. “Why are we doing that? We’re just escalating this war and making it worse. That should not have been allowed to be done. Now they’re doing not only missiles, but they’re doing other types of weapons. And I think that’s a very big mistake.”

McConnell’s critique of Trump’s foreign policy record and worldview follows the president-elect’s decisive electoral victory over Democratic presidential nominee Kamala Harris, marking the first time a Republican candidate won the so-called popular vote since 2004.

McConnell was reportedly one of the four senators who blocked former Republican Florida Rep. Matt Gaetz’s bid to serve as Trump’s attorney general and has not yet met with Trump’s defense secretary pick, Pete Hegseth, or his director of National Intelligence nominee Tulsi Gabbard.

Although McConnell has stepped down from Senate GOP leadership, he has vowed to use the remainder of his time in the Senate to push back against Trump’s foreign policy worldview. As the incoming chair of the Senate Appropriations Defense subcommittee, the Kentucky Republican will have a prominent platform to advocate for a larger defense budget and increased military aid for Ukraine, the Daily Caller reported.