U.S. and Polish soldiers gather near their tanks after a live-fire exercise in Zagan, Poland, on Jan. 30. (Kacper Pempel/Reuters)

— On a snowy field in southwest Poland, U.S. tanks and troops gathered on Monday to defend against a resurgent Russia that President Trump wants to befriend.

The major new deployments of tanks and other heavy equipment will fan out to nations on the Russian frontier this week, part of the largest infusion of U.S. troops to Europe since the 1991 breakup of the Soviet Union. But the long-planned effort comes at the most unsettled time for U.S.-European relations since World War II, with Trump questioning old alliances and seeking to build bridges to the Kremlin.

When President Barack Obama committed the troops, about 3,500 in all, to Europe last February, then followed up with additional commitments to NATO over the summer, they were a bipartisan expression of support for U.S. allies at a moment of heightened fear about Russia.

Now, however, they are coming despite the White House, not because of it. Eastern European ­nations say they fully trust Washington’s commitments — but the jubilation of the summer has been replaced by concern over Trump’s overtures to Russian President Vladimir Putin. NATO leaders acknowledge that the alliance will be rocked if Trump abandons the troop deployments.

The uncertainty has led to an unusual gap between Trump’s rhetoric and that of nearly the entire military establishment underneath him.

“It was the Russian invasion of Ukraine and the unlawful annexation of Crimea” that forced the deployments, said Lt. Gen. Ben Hodges, the commander of U.S. Army ground forces in Europe, ahead of a frigid Monday ceremony on a military exercise range outside the Polish town of Zagan, where a Polish military band played “The Star-Spangled Banner” to welcome the American troops.

“The last American tank left Europe three years ago because we all hoped Russia was going to be our partner. And so we had to bring all this back,” Hodges said.

Trump has offered mixed messages on NATO. He called the alliance “obsolete” in an interview days before the inauguration. But Defense Secretary James Mattis called NATO Secretary General Jens Stoltenberg on his first full day on the job last week, praising “the fundamental and enduring value of NATO for the security of both Europe and North America,” according to NATO.

Later in the week, British Prime Minister Theresa May stood by Trump’s side and attempted to force the issue, saying he had “confirmed that you’re 100 percent behind NATO.”

But Trump has been far warmer to Putin since his election than the leaders of bedrock U.S. allies, saying that the Kremlin is a key partner in the battle against the Islamic State and describing the authoritarian Russian as a strong leader. 

Trump and Putin spoke for an hour Saturday, initiating a new era in U.S.-Russian relations. But the leaders barely mentioned the primary irritant between the West and Russia, its 2014 annexation of Ukraine’s Crimean Peninsula and subsequent fueling of a separatist war in eastern Ukraine, according to officials briefed on the call.

The uncertainty has weighed on Eastern European leaders who have welcomed the international deployment of several thousand troops to their nations.

Any reversal of deployments “would be an issue of concern to us,” said Ojars Kalnins, head of the foreign affairs committee in Latvia’s Parliament. Privately, European politicians, diplomats and security officials say that a rollback of U.S. troop commitments would be a seismic shift for NATO that could upend the alliance. But most say they do not think Trump will reverse the flow, saying that what truly counts are the boots that are currently touching down on European ground.

“This is a substantial deployment, with heavy formations for the type of warfare one could expect if there was a crisis in Europe,” said Fabrice Pothier, a former senior NATO official who is a senior research fellow at the Atlantic Council, a Washington-based policy center.

But if Trump decides to alter the deployments, that would fundamentally change European defense calculations, Pothier said. 

“Everybody is going to run for cover,” he said. “It would lead to a more fragmented, more unstable Europe. It’s a lose-lose both for the U.S. and the Europeans.”

Monday’s exercises involved the U.S. Army’s 3rd Armored Combat Brigade Team, 4th Infantry Division, which arrived in Germany this month with 87 Abrams M1A1 tanks, 20 Paladin artillery systems and 136 Bradley Fighting Vehicles. The troops will spread across Eastern Europe, fanning into the Baltic nations, digging into Poland and also deploying to Romania, Bulgaria and Hungary.

When the brigade finishes its deployment in nine months, it will be followed by another group of similar size, a rotation that the Pentagon currently expects to maintain on a near-permanent basis. 

Separately, Britain, Canada and Germany are sending battalions to Estonia, Latvia and Lithuania as part of a commitment made at a NATO summit in Warsaw in July. Those troops, along with a U.S.-led battalion in Poland, will take up their positions this spring.

In Zagan, the site of a vast Communist-era artillery training field, there was little explicit acknowledgment of the new questions over NATO’s future. But phrases that would have been unexceptional before Trump’s November election victory took on new meaning after his inauguration.

“An attack on any of us is an attack on all of us,” said Paul Jones, the U.S. ambassador to Poland and the senior representative of the Trump administration at the event.

Polish leaders said they were delighted to be able to choose their friends, something they said was not possible during more than four decades of communist rule.

“Thirty years ago, which is not that long in history, we had units here in Zagan which we were forced to treat as allies,” said Polish President Andrzej Duda, referring to Soviet army troops. “And today we have in Zagan allies who symbolize freedom.”

After the celebratory speeches, Polish and U.S. tanks and heavy artillery were part of live-fire exercises intended to show that they could work together to fend off a common, unnamed enemy. Explosions and gunfire rang out across a deforested training plain, covered in the snow and mud of a Polish winter.

But there was an easy way to distinguish the nations’ units: Polish tanks and artillery units were painted forest green, while the U.S. tanks were desert sand, a symbol of American military preoccupations over the past 15 years.

No matter the winds of change in Washington, the U.S. military appears to be making plans for a long-term shift in focus toward Europe.

“I’ve asked the Army to send over some green paint,” Hodges said.