Could FDR have been impeached?

[Jaenera Targaryen]

If FDR ordered the US Navy to conduct a surprise attack on a nation the US was not at war with, and not even in a Cold-War type confrontation, he'd be in a lot of trouble regardless of the outcome.

If he somehow anticipated the attack on Pearl Harbor, and had the Navy ambush the Striking Force as it approached Hawaii, then it would be clear that Japan intended to attack the US and FDR's action had merely pre-empted them. That he could do without blowback.

But sending US ships thousands of km to attack Japanese ships in harbor without a declaration of war would be very different. Historically, Presidents have sent American forces into action without declarations of war many times, and frequently without any kind of Congressional approva. But- nearly always on a small scale, against bandits, or pirates, or guerrillas, or in small countries, especially those near the US. Such "police actions" have been allowed as part of Presidential discretion.

Sending the main force of the Navy to attack a Great Power would be much bigger act, and would be regarded as a gross usurpation of power. If FDR could present authoritative, convincing evidence that Japan was actively preparing to attack the US... That might get him enough support to avoid impeachment.

FDR might try presenting the evidence to a select group of Congressional leaders just before the attack went in, asking for their unofficial approval, (Unofficial, since a vote by Congress could not be secret.)

Even so, a lot of people would be very disturbed. Many would say that the US had put itself in the wrong; that the US should have waited till Japanese ships approached US possession.

Without such a presentation and approval, the reaction would be enormous. It would be comparable to the reaction to FDR's "court-packing" plan to expand the Supreme Court, which alienated even some of his most enthusiastic New Deal allies.

FDR would probably be impeached, but not convicted. If the evidence for intended Japanese attack was weak or ambiguous, he might be convicted. If the attack was a complete success, that would help him.

Let's put it on the middle ground. FDR or the US Admiralty don't know about Operation Z, but they know of the Japanese plan to draw the USN to the West Pacific and defeat in decisive battle at the Philippines. The attack succeeds in sinking all of Japan's battleships at harbor, along with a number of destroyers and cruisers. However the Japanese carriers were holding exercises at sea nearby, and succeeded in launching one counterattack, sinking two carriers while their planes were gone and before the Pacific Fleet could escape.

So the Americans know Japan was planning for an eventual war with them, but not in the near future. They also succeed in destroying the Japanese battle line, but they fail to sink the Japanese carriers, which manage to sink two American carriers in self-defense. How does FDR handle this in front of Congress?