April 2 (UPI) -- Two Republican members of the U.S. Senate have broken with President Donald Trump on his threat to leave NATO because it would fulfill the "greatest dreams" of Russia and China.

Sen. Thom Tillis, R-N.C., on Tuesday joined Sen. Mitch McConnell, R-Ky., in opposing Trump's latest comments about possibly leaving the post-World War II alliance that was formed as a bulwark against fears of Russian aggression in Europe.

Trump has long aired grievances about NATO -- starting during his first term as president -- but has ratcheted up his complaints about the alliance since the United States and Israel started the now month-old war in Iran because none of its members have assisted with the conflict.

In a joint statement with Sen. Jeanne Shaheen, D-N.H., with whom he co-chairs the Senate NATO Observer Group, Tillis pointed to the importance of the alliance to U.S. economic and military security.

"NATO is the strongest and most successful military alliance in history," Tillis and Shaheen said in the statement. "It promotes economic stability and protects economic stability and protests our most important trading relationships."