Is there any circumstances that might cause Manchin to bolt, if he is re-elected? By bolt I mean change party affiliation.
Not with the Republican party growing increasingly reactionary and extreme. Manchin supports some gun control, is to the left of most Republicans on most social issues and definitely on economic issues. He was a Democrat while the main Republican contenders were Mitt Romney and John McCain, he won't bolt when it's controlled by extremists. And no, contrary to what you're probably going to respond, he won't bolt because Democrats are becoming "sjw socialists", because that's just not the case.