That much is obvious. What's also obvious, to me, is that the birther movement was completely marginal until early 2008, when it gained enough traction among the racist fringe of Clinton's supporters that Snopes finally had to publish an article debunking it.
And what's also obvious to me is that while Clinton did not specifically propagate birtherism, her 2008 campaign was notoriously, astonishingly racist. It was marred by a well-documented series of innuendo and dog-whistles, and as Ryan Cooper notes, "the attempt to play on racist attitudes through constant repetition and association was unmistakable". And there's significant reason to believe that this broader effort to wield racism against Obama was quite deliberate.
None of this is particularly controversial. But it seems to me that, once we acknowledge the racism of Clinton's 2008 campaign, we have to accept that it helped to normalize and popularize racism as a political weapon against our first black president. When Hillary stoked the Jeremiah Wright controversy and when Bill made his notorious comments about Jesse Jackson, they signaled to America that racist attacks on Obama were acceptable and even respectable. They lent such attacks a veneer of bipartisan credibility and gave Republicans who wanted to escalate even further plausible deniability.
Consider, for example, the notorious case of Clinton campaign fundraiser Geraldine Ferraro, who insisted that "If Obama was a white man, he would not be in this position...He happens to be very lucky to be who he is." For her part, Hillary Clinton would only call it "regrettable that any of our supporters, on both sides...say things that kind of veer off into the personal." In response, the Wall Street Journal reported, David Axelrod insisted that
by not further repudiating Ferraro’s remarks the Clinton campaign was sending a “wink and a nod” to her supporters that similar comments will be condoned.
And sure enough, that's exactly what happened: well after Obama secured the nomination, self-identified "Party Unity, My Ass" (PUMA) Clinton supporters who defected to McCain were echoing Ferraro almost verbatim and calling Obama an affirmative action president.
Should we be surprised that Axelrod was right? No, Clinton did not start birtherism. But she and her campaign gave a wink and a nod to racists, and predictably, this taught Americans that similar racist nonsense would be condoned.