Pretty Americentric line of thought considering us dirty gaters have international "membership", but this also applies to the West in general.
Call it China or the Globalists -- 'and' is probably more appropriate, but there's been a deliberate decades long attack on our educational institutions, our government, our economy, the Christian religion, our borders, Communist infiltration of key positions in government and industry, etc. etc. etc.
And it's been so effective, I just don't see a reversal of course. Even if the moderate collective pulled the wool from their eyes and took action, we're still due for an economic implosion as the debt bubble eventually pops, and we'd have to deal with the indoctrinated masses who would violently resist being jacked out of the Matrix.
Personally, by this point I'm not even thinking about saving the republic, but rather what actions will need to be taken to build something better from its ruins.
Has the pendulum ever swung right in the US?
Depends on the issue. Generally, it has slowed its leftward swing and sometimes been stilled for a period of time, but has not swung right in a long time.
There was a right-leaning backlash in the 1980s that slowed the pendulum swing but ultimately went nowhere since Reagan and HW Bush were sellout neoliberals underneath their thin veneer of nationlist rhetoric.
Before that, maybe a few years post-WW2 from the late forties to mid fifties.
The last true "rightswing" of the pendulum on a national scale would probably be somewhere around the time of the Second Great Awakening, and even then that was mainly on social issues, not neccesarily policy or economic issues.
I think after we "won the west" in the 1890s, was when the leftward shift really began. They replaced Manifest Destiny rhetoric with economic and social rhetoric that had a leftward slant.