U.S. Republican presidential front-runner Donald Trump, if elected, would "pick fights" with South Korea and Japan over the cost of American troop presence in the allies, the Washington Post said, warning of foreign policy troubles Trump's presidency could bring about.

"The Trump foreign policy ... is that the United States' long-standing relationships and alliances are stacked against it, and that they must be downgraded, renegotiated or abandoned," the paper said in an editorial, titled "A President Trump would weaken the United States abroad."

"Mr. Trump would pick fights with Japan and South Korea over their purported insufficient payments for the U.S. troop presence in those countries, even though each country funds about half the non-personnel costs -- and even though the costs of dealing with a U.S.-free Asia, in which Japan and South Korea might go nuclear for fear of China and North Korea, could be higher by far," it said.

The billionaire real-estate mogul has repeatedly made unfounded accusations that South Korea pays almost nothing for the upkeep of the 28,500 American troops stationed in the country to help defend the ally against North Korean threats.

Seoul has long shouldered part of the burden needed for the U.S. troop presence. In 2014, the two countries renewed their cost-sharing agreement, known as the Special Measures Agreement, with Seoul agreeing to pay 920 billion won for the upkeep of the U.S. troops per year, a 5.8 percent increase.

The presence of U.S. troops in South Korea is a legacy of the 1950-53 Korean War, which ended in a truce, not a peace treaty, leaving the divided peninsula still technically at war. Moreover, the American military presence on the peninsula is seen as in line with U.S. national interests in a region marked by a rising China.

As Trump looks increasingly likely to be the Republican nominee after the "Super Tuesday" primaries and caucuses earlier this week, concerns about his possible nomination have been growing stronger within the Republican Party.

On Wednesday, more than 50 Republican national security leaders, including former Deputy Secretary of State Robert Zoellick, issued an open letter saying they are united in opposition to a Trump presidency that they said would "make America less safe" and "diminish our standing in the world."

"His insistence that close allies such as Japan must pay vast sums for protection is the sentiment of a racketeer, not the leader of the alliances that have served us so well since World War II," they said in the letter.

On Thursday, former Republican presidential nominee Mitt Romney delivered a blistering attack on Trump, saying his domestic policies would lead to recession and his foreign policies would make America and the world less safe.

"Let me put it plainly, if we Republicans choose Donald Trump as our nominee, the prospects for a safe and prosperous future are greatly diminished," Romney said. (Yonhap)