WARSAW — As the United States ramped up warnings of a Russian attack, and as Western allies called for unity against aggression, the leaders of two NATO members bordering Ukraine headed for a gathering in Madrid over the weekend called “Defend Europe.”

But instead of tackling the Russian threat to Europe’s eastern frontier, the meeting attended by the prime ministers of Poland and Hungary, Mateusz Morawiecki and Viktor Orban, focused on what the populist leaders cite as their most pressing threats: immigration, demographic decline and the European Union.

Even as the two NATO members rely on the alliance for their security, the pressing in Madrid of issues that have long driven a wedge between them and the United States and the European Union highlighted the extent to which domestic political concerns remain at the forefront of their calculations.

The meeting, which brought together populist, and for the most part, Kremlin-friendly, standard-bearers from across Europe, also underlined just how much those politics have blurred what the United States views as a clear-cut case of bullying by Russia, a nuclear-armed autocracy, against Ukraine, a vibrant, albeit highly dysfunctional, democracy.

Mr. Orban, the Hungarian prime minister, travels to Moscow on Tuesday to meet President Vladimir V. Putin. France’s far-right presidential candidate Marine Le Pen, an outspoken fan of the Kremlin, was also at the two-day conclave, as was Austria’s far-right Freedom Party, which has long called for an end to European sanctions imposed on Moscow over its 2014 annexation of Crimea and military incursions into eastern Ukraine.

A declaration issued after the Madrid gathering made no mention of Ukraine, though it did lament “Russian aggressive actions on Europe’s eastern border.” It instead stressed the need to form a united front in favor of “family policies,” Christianity and keeping out immigrants. The European Union, the statement said, had become “detached from reality,” leading to “demographic suicide. ”

Poland is a country with a long and traumatic history of Russian aggression. That it would join a gathering focused on attacking the European Union at a time of crisis on its eastern border highlighted just how much the governing party sees Brussels as a threat.

Poland regularly denounces Moscow and supports the presence on its territory of around 4,500 American troops and a U.S.-run missile defense installation. But, incensed by E.U. criticism of its restrictions on judicial independence, L.G.B.T.Q. rights and other issues, the governing party has increasingly turned its fire on Brussels.

“Polish foreign policy has been completely subjugated to domestic needs and is now all about stopping interference from the European Union,” said Roman Kuzniar, a professor at Warsaw University who advised his country’s previous pro-European government.

While tiny Baltic States have sent arms to Ukraine and worked to forge a united front against Moscow, Poland, the region’s biggest and most militarily powerful country, has “been very passive and has had nothing serious to say,” Professor Kuzniar added.

After weeks of dithering, Polish authorities said on Monday that they would offer “defensive weapons” to Ukraine. Prime Minister Morawiecki, who travels to Ukraine’s capital, Kyiv, on Tuesday, expressed his “unwavering support” for Ukraine against “Russian neo-imperialism” that he said threatened “destabilization” of the European bloc.

Jacek Bartosiak, the founder of Strategy and Future, a research group, defended the government’s caution, saying that Poland has too much at stake in Ukraine to risk hasty gestures. Poland, he said, “is the most important piece of the puzzle in the game being played around Ukraine.”

The scrambling of foreign policy by domestic politics mirrors a similar phenomenon in the United States, where the Republican right has challenged the Biden administration’s support for Ukraine and asked whether Russia might be a more worthy cause.

Few in Poland voice sympathy for Russia. But, there is also deep wariness about Ukraine, the western part of which belonged to Poland before World War II, particularly among nationalists who view as genocide the massacre of tens of thousands of Poles by Ukrainian nationalists during the conflict.

“Anti-Ukrainian feeling is the ABC of Polish nationalism,” said Marek Swierczynski, a security expert at Politika Insight, a research group in Warsaw. “Everything in Poland these days has become so politicized,” he added, noting that Law and Justice has been reluctant to embrace Ukraine too closely because “part of their base may turn against them.”

Hostility toward Russia generally cuts across political divisions but has been overshadowed by hostility toward Brussels, the ruling party’s favorite bugbear.

Jarosław Kaczyński, the head of Law and Justice and Poland’s de facto leader, fulminates regularly against the European bloc, claiming in December that it was becoming a German-led “Fourth Reich,” but has said nothing publicly about the Ukraine crisis.

Mr. Kaczynski’s liberal critics note that his emphasis on defending traditional Christian values against what he views as decadent intrusions by the European Union is almost indistinguishable from the Kremlin’s own favorite propaganda trope.

But while standing on the Kremlin’s side in Europe’s culture wars, nationalist populists in Europe are bitterly divided over whether to reject or embrace Mr. Putin, a rift that has hobbled their efforts to make common cause. At the Madrid gathering, which followed a similar event in Warsaw in December, Mr. Morawiecki, the Polish prime minister, pushed hard to get a reference to Russian aggression included in the final statement. Ms. Le Pen objected and issued her own statement that made no mention of Russia.

George Simion, the leader of a right-wing Romanian political party, described the meeting as a “disaster” because of divisions over Russia, which he views as a threat blocking his own pet political cause, the union of Romania with neighboring Moldova, a territory seized by Moscow in 1940.

Poland’s high-level presence at such a gathering caused dismay among critics of Law and Justice, particularly the opposition leader Donald Tusk, a former Polish prime minister who emphasized outreach to Ukraine and close relations with the European Union.

Denouncing the Madrid meeting as “anti-Ukrainian and pro-Putin,” Mr. Tusk had urged the prime minister not to attend. Among the parties in attendance was a far-right Estonian outfit whose leader has campaigned for elections with the anti-immigrant slogan: “If you are Black, go back!”

Mr. Orban, the Hungarian prime minister, has a long record of cozying up to Moscow and quarreling with Kyiv, particularly over its policies toward ethnic Hungarians in Ukraine. Like Law and Justice in Poland, his Fidesz party has built its political brand around combat with the European Union, from which both countries have received billions of dollars in aid but which serves as an easy punching bag in domestic political battles.

Facing a tough election in April, Mr. Orban has gone further than any other European national leader in reaching out to Moscow and demonizing the European bloc.

His opponents on Monday urged him to cancel his Tuesday visit to see Mr. Putin for talks on gas contracts and the expansion of a Russian nuclear power project in Hungary.

Peter Marki-Zay, the standard-bearer for an unusually united opposition camp in the April elections, said the Moscow trip meant that “Hungary has betrayed its Western allies” and “betrayed the country’s thousand-year-old dream of Western integration.”

Aside from the Baltic States, which have been steadfast in their support for Ukraine, Europe’s formerly Communist eastern fringe has sent mixed messages, pledging loyalty to NATO, which now includes most former members of the defunct Soviet-led Warsaw Pact, but at times voicing distrust of Ukraine.

In the most abrupt rupture with NATO’s position of solidarity with Ukraine, President Zoran Milanovic of Croatia, which joined the alliance in 2009 along with Poland, last week said Ukraine should never be admitted to NATO, a view heartily shared by Moscow. In the event of a Russian attack on Ukraine, the president said, “Croatia must get away from it like from a fire.”

His comment, however, was driven less by the crisis over Ukraine than domestic political squabbles with Croatia’s prime minister, Andrej Plenkovic, who belongs to a rival political party and has voiced strong support for Ukraine. The prime minister this week issued a statement noting that Ukraine deserved support as one of the first countries to recognize Croatia as an independent country after it split from Yugoslavia during the Balkan wars of the early 1990s.

The history of past wars weighs heavily on governments across the region, where gratitude for past support jostles with bitter memories of betrayal, often by the same people.

In Poland, Poles massacred by Ukrainian nationalists during World War II compete with earlier memories of how soldiers from Ukraine helped Poland defeat invading Soviet troops in 1920 on the banks of the Vistula River near Warsaw.

“Our history is very difficult,” said Mr. Swierczynski, the Polish security expert.

Benjamin Novak contributed reporting from Budapest and Anatol Magdziarz from Warsaw.