WASHINGTON — Republicans control Congress so President Donald Trump’s pledge to boost the Pentagon budget by tens of billions of dollars should be a sure bet.

It’s not.

Trump faces skeptical Democrats whose support he’ll need and resistance from fiscal conservatives opposed to repealing a 2011 law that set firm limits on military and domestic spending. Unless the president figures out a way to mollify the disparate camps, he’ll have a tough time delivering on a signature campaign promise to rescue the armed forces from a festering financial crisis.

Senior U.S. commanders have flatly warned that the spending caps set by the Budget Control Act are squeezing the armed forces so hard that the number of ready-to-fight units is dwindling. That means beating powers such as Russia or China is tougher than it used to be as aging equipment stacks up, waiting to be repaired, and troops don’t get enough training.

Gen. Daniel Allyn, the Army’s vice chief of staff, startled many lawmakers when he testified recently that just three of the service’s 58 active-duty and reserve brigade combat teams are ready to fight at a moment’s notice.

Allyn and other four-star officers pleaded during separate hearings in the House and Senate for the spending limits to be repealed, clearing the way for the bigger budgets they say are needed to stop the military’s readiness for combat from decaying further.

The average age of Air Force aircraft is 27 years, according to Wilson, who added that more than half of the service’s inventory would qualify for antique vehicle license plates in Virginia. On top of that, the Air Force is short 1,500 pilots and 3,400 aircraft maintainers, he said.