That "Declaring War" is a function of Congress, passed as a standing law, and as such becomes the REQUIREMENT of a President to execute to the best of his ability. The only reason that REPUBLICAN PRESIDENTS never declare war, when they go to "war" is because Congress has not ordered them to, and as such, they are most most of the time acting outside the boundaries of Constitutional Law.
Bush I carried out the declaration of war against Iraq, (limited to removing the Iraqi land army from Kuwait), after the Government in Baghdad declared war on the United States. If I remember correctly. That limitation on combat action was why the American Army didn't invade Iraq, sack Baghdad, and topple the sitting government there in 1991, because it was a limit on Presidential prerogative that Bush the First actually had the good sense to respect, even if he disagreed with it (which he didn't). Even then-Sec.of Defense Dick Cheney gave cogent reasons for why the United States didn't want the government in Baghdad destroyed, and they were the same reasons that were later IGNORED by the same team of advisors to Bush the Lesser, and what happened was EXACTLY WHAT CHENEY SAID WOULD HAPPEN in 1991.

Democratic Presidents don't destroy standing Foreign Governments unless Congress MAKES them. That's the difference. THAT'S what your Republican friend was trying to say to you.

If my memory is incorrect, will someone fix that for me please?