It's a mix of selling MIC budget and pandering to racists for votes, but the trickier problem is that both Machiavellian realpolitic schemers and random bigots who hate China can advance with that scheme. If the political landscape shifts, then the random bigots will get weeded out (in favor of different random bigots, this is American politics after all), but if anti-China sabre rattling is politically useful for long enough, then they'll end up in more stable positions of power and continue pursuing anti-China stances, even past the point where those stances were useful.
It's a mix of selling MIC budget and pandering to racists for votes, but the trickier problem is that both Machiavellian realpolitic schemers and random bigots who hate China can advance with that scheme. If the political landscape shifts, then the random bigots will get weeded out (in favor of different random bigots, this is American politics after all), but if anti-China sabre rattling is politically useful for long enough, then they'll end up in more stable positions of power and continue pursuing anti-China stances, even past the point where those stances were useful.