Manchin’s home state of West Virginia backed Trump by a 42-point margin in 2017. By 42 points, West Virginia voters said they supported Donald Trump over Hillary Clinton, and supported his policies and leadership, including, presumably, the health-care bill that Trump wanted to see passed. His colleague, Shelley Moore Capito (R), considered voting against the effort, but ultimately stuck with her party despite being about as moderate as Murkowski.
But at no point did Manchin appear to waver. Same with the other four. Their states backed Trump by an average of 23 points, but Heitkamp, Tester, McCaskill and Donnelly held firm. No on motion-to-proceed, no on the final bill. Had any of them indicated a willingness to jump ship, they’d have been embraced by the president and by Republicans in their home states (at least until reelection), but none did.