It's a little early for there to be a strong sense of regret from Trump supporters (especially those who specifically like him, and aren't just partisan Republicans.) I wouldn't be surprised if, in another year or two, there will be a non-negligible percentage of Trump voters who regret voting for him. It won't be anywhere near 50%, but it might be in the 5-10% range.
By the end of the Trump presidency if he's impeached or is still in the 30s popularity 20% of the Trump voters will have recanted. Nobody likes being on a losing side indefinitely.
I can't vouch for how true this is, but I remember hearing that Hoover retained 80% of his 1928 voters in 1932.
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