Most other first-world countries have solved social issues like legalizing same-sex marriage, improving worker conditions, and solving unequal pay for women. We're the only country that hasn't resolved those problems.
Politically, pretty much most first-world countries are modeled on the U.S Democratic party. I'm not saying that the Democratic party is the best, but if almost all of the first-world countries are already being like the U.S Democratic party, then I actually feel like there's something wrong.
The US is certainly not in the best of shapes as of now with a Congress split between two camps with more stubborn and bull-headed than pouting 2nd graders and a White House that is occupied by a President half of our legislature detests. Are we politically behind? Not quite, but if this stalemate and partisan nature of US politics perseveres, then neither party will gain ground and the country, not party mantras, will suffer. So, the US is not politically behind (politics are all about argument) but it is on the road to being so if nothing changes very soon.