High A tier. Definitely the best foreign policy of any President in the first half of our national existence. His Doctrine was far more urgent than most realize - at that time the Holy Alliance was considering sending an armada across the Atlantic to crush the South American republics, and there was even talk that America would be next. The Adams-Onís Treaty paved the way for further westward expansion. All in all, he tidily finished up the work of securing America's status as a fully sovereign, equal nation that could defend itself and didn't face any immediate threats from other European powers. His Indian policy was the best of any President up to that point. His cabinet selection was excellent, and Adams and Calhoun especially served as a very useful brain trust that served Monroe well. Most importantly of all, he avoided crucial mistakes during a time that was crucial for America's growth and development.
So many things were happening in Latin America that this talk from Europeans who didn't know what was going on was meaningless. Gregor MacGregor was able to pull off one of the greatest scams ever then.