That's not strictly true though. It is in part but especially now where the US system is so divided and polarised and with so much outright hatred between the two main parties, so much so people disown family members over it. Even if the Dems were doing well and the country was prospering the majority of Republicans, especially the evangelical lot and the far right element would still never vote for their own interests. They would still find something to moan about because for many, change in government won't ever truly affect their lives how they we expect it or think they deserve it to be changed.
You're also discounting the fact many Evangelicals will vote simply over issues like abortion or the belief Democrats aren't Christian's because of their "woke" beliefs. The staggering irony of course is that so called woke beliefs are just inclusion, equality and fairness for all which is what we are told as the core teachings of Jesus and the Bible. Although the Bible is absolutely choc full of contradictions it always leaves them an argument or reason to hold their beliefs against others and defend their twisted position.
Back to my point though, it's not just immigration people will blame. As you saw this last election it was immigration, Biden, Kamala, The Dems, Trans people, Drag queens, woke ideology and liberal brainwashing by schools and colleges.
Now the Republicans are in charge it's the rest of the world, China is the latest target with the EU not far behind because apparently, if you weren't aware, Trump has already sorted out all the immigration, egg prices, gas prices and the cost of living crisis issues and anything he hasn't it's Biden's and the Dems fault.
Dems and independents can be equally guilty of this too but I honestly see far more self awareness and acceptance of their party or politicians faults, crimes or mistakes. That's something I have seen less than a handful of times from Republicans and especially MAGA and Q Anon lunatics.