President Trump’s assertion that NATO countries are not carrying their fair share of the security burden rings hollow across military bases in Eastern Europe this month, where 45,000 troops from the United States and 23 other countries are staging war rehearsals for a Russian invasion.

Eighteen exercises are underway this summer in the Black Sea region, an area that has grown especially nervous about Russia’s aggressive posture.

U.S. military leaders do not expect an imminent invasion, but they understand why countries along the Russian border are jittery. These exercises should help them prepare to fight back if and when Russia threatens them, said Lt. Gen. Ben Hodges, commander of U.S. Army Europe.

“I don’t think that’s likely to happen, but it has happened,” Hodges said. “And certainly anyone who lives close to that area, from Finland and Sweden all the way down to Romania, believes it is possible.”

Hodges spoke Tuesday from Bezmer Air Base, Bulgaria, in a live webcast hosted by the Association of the U.S. Army.

In the largest of the 18 exercises, dubbed Saber Guardian, 14,000 U.S. soldiers are participating. Other troops came from Armenia, Bulgaria, Czech Republic, Germany, Croatia, Georgia, Greece, Hungary, Lithuania, Macedonia, Republic of Moldova, Montenegro, Netherlands, Poland, Romania, Serbia, Slovakia, Slovenia, Turkey, Ukraine and the United Kingdom.

The naval piece of the combat rehearsal is called Sea Breeze, co-hosted this year by the United States and Ukraine. Air, land, sea, and amphibious forces from 17 nations will simulate maritime interdiction operations, air defense, anti-submarine warfare, damage control tactics, search and rescue, and amphibious warfare.

Patriot anti-missile batteries were deployed in Lithuania for the Tobruk Legacy exercise, which focuses on long-range anti-aircraft and missile defense.

Hodges said these drills should not be viewed as provocative acts but as “deterrence.”

“We want to be ready,” he said. “We are practicing how we would mass power and assemble multinational teams quickly so our political leaders have some options.”

A sense of urgency is especially acute among the three Saber Guardian host nations: Hungary, Bulgaria and Romania. “They are all in on this thing,” said Hodges. “These countries are completely committed.” The public there has welcomed U.S. soldiers, he added. “I’ve been very pleased with that.”

U.S. allies are fretting over Russia’s upcoming military exercise, called Zapad. About 3,000 Russian troops and 800 tanks will be in Belarus later this year to rehearse and train for a potential confrontation with NATO. “There is anxiety about the Russian exercise,” said Hodges. This will be the first Zapad since Russian’s annexation of Crimea in 2014.

The incursion into Crimea was the event that forced NATO to rethink its security posture. “Russian aggression in the 21st century has pushed warfare into unfamiliar territory,” Army officers Amos Fox and Andrew Rossow wrote in a recent Institute of Land Warfare white paper.

In conflicts in Chechnya, Georgia and Ukraine over the past decade, Russia has perfected “hybrid warfare” tactics, they noted.  “It is a whole of government approach” that includes covert action, manipulation of public opinion and cyberwarfare.

The exercises in Eastern Europe are important for the U.S. Army as well, said Deputy Commander of U.S. Army Europe Maj. Gen. Timothy McGuire.

“What do we do in a crisis?” he said via webcast from Bulgaria. The U.S. military for a long time has not trained for the type of war that it would have to fight against a sophisticated enemy like Russia. “We have to bring back that toughness,” McGuire said. “We are trying to get back to being agile,” he said. “The days of going to a FOB [forward operating base] with three meals a day provided by [military contractor] KBR are over.”

One of the challenges is logistics, he said. “You’ve heard the saying: Tactics are for amateurs, logistics are for professionals.” The U.S. Army has three combat brigades based in Germany, so moving troops and supplies to Eastern Europe would require careful planning. “We have to get diplomatic clearances from nations,” said McGuire. “We’ve had friction at the borders; the coordination is not as solid as it should be.” Even routine checkpoints can hold up supply convoys.”

In the United States, meanwhile, the debate continues over how much of the Army should be permanently based in Europe.

The presence there was downsized dramatically after the Obama administration in 2012 adopted a “pivot to Asia” strategy that deemphasized Europe. Two armored brigades in Europe were eliminated. Two brigades — a Stryker and an airborne infantry — remained.

Priorities had to be reevaluated in the wake of Crimea. An armored brigade and a combat aviation brigade now rotate there for nine-month tours. A study by the Army War College suggested the Army should consider stationing a brigade in Poland.

Most U.S. military leaders have pointed to Russia as their top national security concern. Trump administration officials have not said much on the issue, which is not surprising, as the White House remains embroiled in scandals related to Russian’s meddling in the 2016 presidential election.

Trump’s nominee for principal deputy undersecretary of defense for policy, David Trachtenberg, explained his thinking on Russia last week during his confirmation hearing in front of the Senate Armed Services Committee. “We face no shortage of challenges. Russia has invaded a neighbor whose territorial integrity it pledged to respect, violated its arms treaty commitments, and threaten NATO allies with nuclear attack.”

Sandra Erwin is a national security and defense reporter for RealClearDefense, where this first appeared. She can be reached at [email protected]. Follow Sandra on Twitter @Sandra_I_Erwin.