Strongest country the US can realistically invade in a 4 years timespan?

The US president decides to stage an invasion of another country and wants to pick the mightiest realistic foe. He wants to achieve wincon before the end of his term.

The US population is pretty bloodlusted, but it will not be willing to accept losses in high millions of men. War starts in three months and both sides know about it. The international community disapproves of the invasion, so the US can't use bases in other countries without entering in war with them as well.

The defending population is very determined and can't be easily strangulated economically as there is a number of nations willing to give them very favourable loans.

US is sort of a rogue state anyway by the point, so it doesn't need to care about pretty much any part of the International Humanitarian Law.

It should really be considered that everything is logistically feasible for the US, if it is staging an invasion from the sea.

R1 - no nukes, all mutual defence treaties apply, but exclude the US (=> the rest of NATO is still a compact force)

R2 - no nukes, no mutual defence treaties apply

wincon for the US - hold three biggest cities in the respective country for a span of half a year