Nuclear thermal rockets were developed and certified for manned space flight back in 1968. These were meant to power the manned mission to Mars in 1978 (which was cancelled obviously). https://en.wikipedia.org/wiki/NERVA
It seems like a lot of the things happening at NASA at the moment are an attempt to get back to where they were in the 60s.
You "can't believe" (your words) because your major premise is false. The "'we're the king of the world' attitude/arrogance/bs" is largely a figment of your imagination. A higher percentage of South Africans probably have that view about SA than do Americans about America.
As to launch capability: The USA took a policy decision more than a decade ago to encourage the development of private launch vehicles rather than have NASA do everything. That is why, when the Shuttle program ended in 2011, no NASA-driven manned launch vehicle program was established. In other words, it's a deliberate and intentional act, a sign of strength rather than weakness. No other country has a private launch vehicle program like Blue Origin and SpaceX.
Of course the USA has several operational launch systems like Atlas-V, Pegasus, Minotaur/Taurus, Delta II and IV, now used for unmanned launches, which are much more frequent than you think.
Without a new government-funded manned program since the now-old ISS, the USA government decided years before the Shuttle program ended that it would use Russian capabilities for manned orbital injections to the ISS (a program conceived in the late '80s, with first launch in late '90s), while encouraging and supporting private (non-gov) domestic programs. Don't forget the I in ISS - signing for Russian launchers was in fact the USA's way of funding the maintenance of Russian capability after the collapse of the USSR.
For the USA it's much more a case of "been there, done that, no need to continue doing it". A conscious choice. It allows NASA to focus on aeronautical and space technology research and development - like this nuclear engine - rather than maintaining its own manned launch capability.
They do have various launch vehicles, although these are largely powered by high pressure rocket engines that they buy from the Russians.
The US has a new launch vehicle vehicle under development which now looks like it will have it's first flight in 2020. This vehicle will reduce the reliance on Russian engines by using a derivative the RS-25 engine from the space shuttle (which in turn was adapted from the Saturn V moon rocket).