Hungarian Prime Minister Viktor Orban during a meeting in the Oval Office with President Donald Trump on May 13, 2019, in Washington, DC.Mark Wilson/Getty Images

Hungary's nationalist prime minister, Viktor Orbán, is traveling to Florida on Thursday to meet with former President Donald Trump following a NATO summit in Washington, despite unease from the White House.

Orbán publicly endorsed Trump's candidacy in this year's presidential election and hopes that the Republican can finally bring a close to Russia's war in Ukraine.

The meeting in Mar-a-Lago, Orbán's second since March, is the last stop on what he's declared a "peace mission" directed at finding a path to end Russia's war in Ukraine.

White House national security adviser Jake Sullivan signaled concern that a Trump-Orbán meeting would run counter to Ukraine's interests, saying:

"The U.S. position-the Biden administration position-is nothing about Ukraine without Ukraine."

"Whatever adventurism that is being undertaken without Ukraine's consent or support, you know, is not something that's consistent with our policy, the foreign policy of the United States," Sullivan told reporters, adding that he "can't speculate as to what Orbán is up to exactly."

The European Union's longest-serving leader has become somewhat of an icon to conservative populists for championing what he calls "illiberal democracy," which includes restrictions on immigration and LGBTQ+ rights, according to ABC News.

During the NATO summit on Thursday, Finnish President Alexander Stubb chastised the Hungarian Prime Minister for his visits to Russia and China.

EU leaders rushed to clarify that the trips were not endorsed by other European leaders.

"I'll say it out loud; I don't think there's any point in having conversations with authoritarian regimes that are violating international law," Stubb said.

"He can do it on his own behalf. But I fundamentally disagree with doing that. I simply do not see the purpose."

All the while, Orbán revealed his firm belief that a new Trump presidency is the "only serious chance" for an end to the war in Ukraine.