I don't think US will dissolve, stagnate, or collapse, but definitely facing imperial overstretch.
However, I do think as the US demographics increasing shifts away from Whites, with racial/ethnic minorities becoming the majority by 2050, that the huge minority population (blacks/Hispanic/Asians) will elect more who support more inward social welfare policies rather than expensive wars and bases abroad. Military spending will be reigned in by more populist, anti-war, and progressive candidates that seek to invest at home, rather than maintaining Old White Man's dream of imperial hegemony.
US could very well become more inward facing and spend more on social welfare (increasing or expanding Medicaid, Medicare, social security reform) that will require drastic cuts to military defense budget and reduce imperial overstretch.
TLDR: Minorities will overtake whites by 2050, and shifting demographic will result in less military spending and imperial overstretch as minorities tend to be more progressive and anti-war compared to Old White Man Imperialist, which is a dying breed.