The truth is that there isn’t a huge correlation between the sophomore numbers and political resilience. Both Bushes had sky-high approval numbers their second year in office, and one lost re-election after fending off a primary challenge, while the other narrowly survived re-election, despite avoiding a primary challenge. Meanwhile, Reagan (79 percent) and Nixon (82 percent) both had pretty average numbers their second year among Republicans, and both went on to win huge landslides.
Trump’s popularity with Republicans is really just pretty average. There is little doubt that the intensity among his strongest supporters is high, but this asterisk is overwhelmed by another important caveat. As Gallup notes: “Fewer Americans identify as Republicans or say they are Republican-leaning independents than did so in November 2016, the month Donald Trump was elected president.”
It may be that Trump is popular among people who identify as Republicans, simply because the Republicans who don’t like him are… no longer Republicans.