George W. Bush is still very popular among Republicans, and his words and actions can still make a difference. Which is why he should endorse Kamala Harris, and tell other Republicans to join him in voting for her.
Most Trump supporters won't be swayed, because they are essentially following him like a cult leader. But could Bush convince a percent or two to switch? Most definitely. And in a close election, that could make the difference.
Huge numbers of prominent Republicans (including Bush's VP, Dick Cheney) have already done so, and Bush needs to as well. But time is short, and Bush needs to act now to make a difference. So he needs to decide -- will he put country over party? Tell him to do it.
Tell George W. Bush to endorse Kamala Harris and encourage other Republicans to do the same