I know some long-time Liberals from another web-site that were very bitter about how Obama ripped Hillary during the 2008 campaign. But Obama did what he had to do to win the nomination and his attacks are all on YouTube. Later of course, when it was her turn to be anointed, all was forgiven and Obama's attacks were buried in the sand as suddenly those things didn't mean anything anymore (especially her vote in favor of the Iraq War Resolution which Bernie opposed, giving a very eloquent and rational speech back in the day explaining why).
The ability of Democrats to effectively "eliminate" past statements and positions is really remarkable. I'm no Trump lover and didn't like how he talked about illegal immigration. However, in the 1990s, plenty of Democrats made statements about illegal immigrants that were every bit as inflammatory, but those were buried, allowing them to get righteous about it.
On another front, "Birtherism" is often treated as a racist conspiracy by Trump and Tea Partiers, but of course, they didn't start birtherism. Sidney Blumenthal did on behalf of Hillary Clinton.
And of course Trump got ripped for going after white working class voters (the so-called "deplorables"), but who was going after them in 2008 with much more racially-charged rhetoric? Hillary Clinton, who was proud to have the support of "hardworking white Americans." That's George Wallace-level stuff and would be an immediate career-destroyer for a Republican. However, after the 2008 Democratic nomination, that stuff was immediately ancient history and never brought up in 2016.
But if you're a Republican? Every dumbass comment will hound you forever, even if you didn't say it. Hell, we still hear about the Willie Horton ad from 1988.