President Donald Trump is tweeting that U.S. policy on North Korea has been unsuccessful, and that America has given “billions of dollars” and received nothing in return.

Trump’s recent tweets on North Korea have prompted questions about whether the president is leaning toward military action. On Saturday, Trump said U.S. “negotiators” were made to look like fools and “only one thing will work.” One prominent Senate Republican, Bob Corker, told The New York Times that he is concerned that Trump could set the U.S. “on the path to World War III.”

On Monday, Trump tweeted: “Our country has been unsuccessfully dealing with North Korea for 25 years, giving billions of dollars & getting nothing. Policy didn’t work!”