Note: This article was updated to include comments from Defense Secretary Mark Esper.

WASHINGTON — Defense Secretary suggested European allies replenish the $771 million meant to shore up Europe’s defensive posture against Russia to fund President Donald Trump’s U.S.-Mexico border barrier.

The announcement is sure to jar European allies, where NATO members have nervously watched the president’s on-again, off-again commitment to the alliance. And it could deal a blow to the narrative among allies that Trump’s boisterous rhetoric should be taken with a grain of salt, given that money has kept flowing from Washington despite trans-Atlantic disagreements.

Half of the $3.6 billion for the border wall would come from dozens of U.S. military construction projects, and the other half would come from projects in Europe and the Pacific. In Europe, there were roughly 40 projects, including training facilities for special forces in Estonia and aviation infrastructure in Germany, Hungary and Slovakia.

Trump is gambling that Congress and allies will eventually restore the money used for the wall, he originally said Mexico would pay for. Defense Secretary Mark Esper suggested that European nations should consider funding projects in their countries.

“The message that I’ve been carrying, since when I was acting secretary to today, has been about the increase in burden sharing,” Esper told reporters in London late on Thursday.

“So part of the message will be ‘Look, if you’re really concerned then maybe you should look to cover those projects for us’ because that’s going to build infrastructure in many cases in their countries,” he added.

As it stands, the maneuver will weaken NATO efforts to deter Russia, feed growing doubts that America would come to Europe’s defense and undermine extensive plans to strengthen NATO’s eastern flank, according to former U.S. Ambassador to NATO Ivo Daalder, now president of the Chicago Council on Global Affairs.

“If you looked at the state of the alliance, you could say the bad news was the president’s rhetoric was problematic for alliance unity, but the administration’s growing investment suggested on a sub-political level the alliance was getting stronger,” Daalder said Thursday. “I can no longer make that argument because we’ve just [signaled] we’re going to cut back on that investment.”

“There may be a good burden-sharing argument to be had, and that reinforcing NATO forces to the east is a shared obligation,” Daalder said, “but the way to do that is to sit down and decide what projects we’ll do, how we’ll do it together and who’ll pay for it―and we did, but now we’re reneging on that deal.”

On Thursday, Trump’s political opponents highlighted how the move follows his recent decisions to hold up $250 million in military aid to Ukraine and to abruptly cancel his trip to Poland to deal with Hurricane Dorian, sending Vice President Mike Pence in his place. Trump had been scheduled to attend an event last weekend remembering the anniversary of Nazi Germany’s invasion of Poland, which led France and Britain to declare war two days later.

Senate Minority Leader Chuck Schumer, D-N.Y., said he found it “galling and appalling” that Trump had secured multiple wins for an “American foe,” Russian President Vladimir Putin, in just two weeks.

“President Trump is, yet again, putting Vladimir Putin before the security of the American people and our allies,” Schumer said. “Cutting the funding used to reinforce our trusted European allies against Russian aggression in order to advance the president’s politically motivated vanity project — that he promised Mexico would pay for — is outrageous, wrong and weakens our national security. Congress will not stand for the president usurping our exclusive power of the purse.”

The targeted projects in Poland illustrate how the seemingly disparate list of smaller construction plans — a runway here, an ammo-storage bunker there — is actually part of a larger strategy, coordinated with NATO, to strengthen Europe’s defensive posture along the eastern front. Putting anything about a “rail extension and rail head” on the table — some line items named — could jeopardize ongoing plans for a cross-border transportation network capable of delivering heavy weaponry deep into Poland.

Such a staging area is envisioned by NATO officials near the country’s town of Powidz. Defense News previously reported that the site’s rail connectivity is vital to the alliance’s plan for a major ground-forces hub.

“Until the railhead is developed, it will be a limiting factor,” retired Lt. Gen. Ben Hodges, a former commander of U.S. Army forces in Europe, told Defense News earlier this year as the Trump administration made a previous attempt to siphon funds away from Polish rail work.

Notably, the Pentagon’s list also curtails funding meant for storage facilities where the service could pre-position “deployable airbase systems,” or DABS. The Air Force had planned to build such warehouses — which would store vehicles, temporary housing and other equipment needed to whip up an expeditionary airfield — at Spangdahlem Air Base, Germany; Sanem, Luxembourg; and Royal Air Force Fairford, England. All have been deferred.

During a July interview, Air Force Chief of Staff Gen. Dave Goldfein pointed to “base-in-a-box” concepts like DABS as an example of how the Air Force could better disperse operations in Europe, as well as other regions such as the Asia-Pacific and Africa.

The delayed programs were largely chosen either because they were upgrades or replacements to existing facilities, a senior defense official told reporters in a Pentagon briefing Wednesday, or because their contract award dates are not scheduled for a year or more.

“We remain committed to supporting our allies and partners,” Air Force spokeswoman Ann Stefanek said. “The affected projects are still authorized and important but have been identified as having delays that would allow their deferment without immediate impact to our mission.”

One official from an allied nation whose project is listed said the U.S. State Department privately communicated that it would work to secure other unspecified funds to avoid construction delays, and that there was no request for it to replace any of the diverted funding. That official expressed frustration at the administration’s mixed messages.

Aaron Mehta of Defense News and Meghann Myers of Military Times contributed to this report.