As Jonathan Chait notes, "Many Republicans started the process believing 1) President Trump did not demand investigation in return for aid but that 2) doing so would be unacceptable. They now believe the opposite on both points." And that's what happened. When they thought he hadn't done it — or at least that that couldn't be proven — they said it would be a very bad, even criminal thing for Trump to do. But now that it's pretty obvious he did it, it's no big deal, just politics as usual and certainly not an impeachable offense.
Mr. Chait has also written this article about why he thinks Bernie Sanders is not the guy to defeat Donald Trump and Willam Saletan wrote this article arguing the same thing. My opinion doesn't mean a whole lot and it is very much subject to change…but right this minute, I think they're probably right. And neither article even mentions another problem, apart from the Socialist label that Sanders has as a candidate: His age and his recent heart attack. There's a lot of grueling campaigning ahead and any medical problems could become a big election issue. Remember how much traction Trump claimed when Hillary had a cold.
But do read Eric Levitz on why the Democratic party needs to embrace or at least accept support from those who may not be as ideologically pure as some of us might like. I think this is a very wise, important observation. It will be of special interest to those who believe (and I don't think I do) that Trump will cry "Foul!' and refuse to accept defeat, and that if we want to get him to actually vacate the Oval Office, he has to be beaten by a landslide. That's all for now.