I believe the people in the GOP who oppose Trump will end up losing their primaries to more extremist candidates in 2018. Plus, the GOP won’t be facing an uphill battle like the democrats will be in the election: there are about 20 seats at stake, and half of them are in red states. So when the new congress convenes in 2019 talks of impeachment will be dead, or at the very least removal will be impossible with 60 senators loyal to Trump.
But the Tea Party was popular back in the day because they were not part of the the status quo. Now they are. Trump was elected for similar reasons the Tea Party was a decade ago: people wanted to shake up the government. But now the Tea Party has been around long enough that people are equally sick of them. Ted Cruz is a Tea Partier and he filibustered and shut the government down. The people don’t want that. That’s why Ted Cruz lost the primary.
People didn’t vote in Trump because he’s extremist. They voted him in because he’s different. If the Democrats can only find some vanilla nobody, then that isn’t going to cut it because people are seeking change.
You have to remember that Barack Obama did get elected. Twice, and by a large margin both times. And we still had racists and white supremacists back then as well. So to say that, because Trump supports will continue to support him, it will single-handedly win the election–that is overlooking other factors involved that lost him the popular vote or won the vote for Obama.