President Donald Trump has quietly transferred more than $200 million from Pentagon counterdrug efforts toward building his long-promised wall along the U.S.-Mexico border, drawing protests from Democrats who say he is again abusing his powers.

The move would shift $129 million to wall construction from anti-drug efforts in Afghanistan - the source of perhaps 90 percent of the world's heroin - along with $90 million freed up by passage of a stopgap funding bill, top Democrats said in a letter to Secretary of Defense Mark Esper.

The Defense Department "was faced with a simple choice: either additional funds be used for their intended purpose, to accelerate our military's efforts to combat heroin production in Afghanistan; or divert these funds to pay for cost increases of a border wall project that does not have the support of the American people," the Democrats wrote.

Senators Dick Durbin of Illinois, Chuck Schumer of New York and Patrick Leahy of Vermont took the lead, noting that the heroin trade is a major funding source for the Taliban and urging the Pentagon to "redouble its efforts to starve the Taliban of a vital funding source and reduce the scourge of heroin abuse in this country and abroad."

Trump has shifted more than $6 billion from Pentagon accounts to pay for border fence construction, considerably more than lawmakers have provided through annual appropriations bills.

Wall funding has been a major source of conflict between Capitol Hill Democrats and Trump as they negotiate agency funding bills each year. For instance, Trump was forced to settle for just $1.4 billion in wall funding in talks this winter. He issued a controversial declaration of a national emergency shortly afterward that allowed him to shift almost three times as much money from military construction accounts to wall building.

A fight over the wall issue is tying up efforts to begin serious negotiations on wrapping up $1.4 trillion worth of agency appropriations by Thanksgiving.

Separately, the Senate is expected to vote Thursday to sustain Trump's veto Tuesday of legislation to reject his emergency declaration.