In this file photo taken on Jan. 14, 2020, U.S. President Donald Trump gestures as he speaks during a "Keep America Great" campaign rally in Milwaukee, Wisconsin. AFP

U.S. President Donald Trump appeared to suggest Monday that the stationing of American forces in South Korea is a form of foreign aid, rejecting the long-held view that the troop presence serves both countries' interests.

Trump's lawyers made the case in the 110-page Trial Memorandum for the Senate's impeachment proceedings against the president. The trial is set to begin in earnest Tuesday, with Trump facing charges of abusing his power by asking Ukraine to investigate Democratic political rival Joe Biden and withholding U.S. military aid to the country in the process.

In the memo, Trump's defense presents arguments for why "Pauses on Foreign Aid Are Often Necessary and Appropriate."

"Placing a temporary pause on aid is not unusual. Indeed, the President has often paused, re-evaluated, and even canceled foreign aid programs," it says.