The United States will withdraw nearly 12,000 troops from Germany in a move that will cost billions and take years

President Donald Trump’s decision to withdraw thousands of troops will take years to execute and potentially cost billions of dollars, according to US defense officials.

The plan to pull US troops out of the former NATO ally has faced wide bipartisan opposition amid concerns that it will weaken the position of the US military vis-à-vis Russia, however the Trump Administration has decided to proceed with the movement.

Approximately 11,900 US troops, a mix of Army and Air Force units, will be withdrawn from Germany to meet Trump’s mandatory limit of 25,000 US forces in Germany, according to a senior US defense official, a number higher than the 9,500 figure that was used when the reduction was first announced.

Authorities said the discrepancy was due to the fact that after a review it was discovered that there were slightly more US troops permanently assigned to Germany, about 36,000, than originally planned.

Of the troops leaving Germany, some 5,400 will “stay in Europe,” but the official will not identify the exact places they will move to, saying that they would only stay in countries that have already hosted US troops in some way. It includes most European NATO members.

The remaining 6,400 forces and their families will be returned to the U.S. And, over time, they will redeploy to Europe on a rotational basis, while remaining permanently on the continent.

Defense officials said this will cost billions of dollars, as new military construction in both Europe and the United States is likely to be required to house the additional troops.

The defense official confirmed that the repositioning will take “months to plan and years to execute,” a timeline first revealed earlier this month by the chairman of the Senate Armed Services Committee, senator Jim Inhofe, who had been briefed on the plan.

The timeline suggests that the plan could be reversed if Trump loses the election in November.

Defense officials say German Defense Minister Annegret Kramp-Karrenbauer and NATO Secretary General Jens Stoltenberg had been briefed on the planned withdrawal, as well as key members of Congress.

Defense officials said Defense Secretary Mark Esper had ordered the repositioning seek to increase deterrence against Russia, strengthen NATO, and support the families of US service members.

However, Trump, who led the measure, said he did so due to Berlin’s failure to meet NATO’s goal of spending 2% of GDP on defense, spending only about 1.38%.

“One of the only countries that has not agreed to pay what they are supposed to pay (in NATO) is Germany. So, I said that until they pay, we will withdraw our soldiers, some of our soldiers, for approximately Later, when we arrive at about 25,000, we’ll see where we go, “Trump said last month.

However, defense officials said on Wednesday that the decision of where to house US troops leaving Germany was not influenced by whether the new host country was meeting the two percent target.

While Germany’s national leadership has been silent on troop cuts, local leaders representing states where US troops are located recently wrote to members of the United States Congress asking them to help reverse the decision.

“We ask that this deep partnership continue and that US forces remain at their locations in Europe and Germany,” wrote the leaders of the German states of Baden-Wuerttemberg, Rhineland-Palatinate, Hesse and Bavaria.

“Therefore, we ask you to support us, as we strive not to break the bond of friendship but to strengthen it and ensure the presence of the United States in Germany and Europe in the future,” added the letter.