Clinton got about 39 percent of white voters in 1992, and 43 percent in 1996.
Hillary Clinton would have to significantly outperform two people who still managed to become President in order for this to happen. It seems very unlikely.
That's a bit misleading though due to the presence of Perot. Bill definitely would've cracked 45% in 1996 if Perot wasn't on the ballot.
But yeah, this would only be plausible if the Republicans nominated a real whackjob. And even then, they would probably still narrowly win whites.