Characterizing all those who voted for trump as racists is a bit much. NO, people did not have to agree with him on "some level" (or any level) when it came to that particular character flaw, as there were simply too many who were incredibly ignorant about that man's history in the first place.
To many of the willfully ignorant, he showed up with a message they wanted to hear about jobs, economy, and making changes in Washington. They thought that the businessman who is not a politician would be there to "shake things up, change things up". While I most obviously disagree with that thought process entirely, I cannot condemn all of his original supporters as racists. I know for a fact a number of people who had supported him who are absolutely, unequivocally not racist. They were simply people who felt that a change was needed, and this asshat was somehow going to be the answer to that.
There are also those who felt that Hillary Clinton was such a horrible proposition for the White House that they were willing to vote for anybody else and that meant Trump. Does that make them racist because they hated Hillary Clinton more than Trump? No. I think it makes them foolish for their choice but that is a different problem.
Now, going forward it would be hard for a trump supporter to claim they know nothing about his Alt Right associations. Now that it is the news that it is, continued support would indicate to me support of his views as well. It does make me wonder how those members of his party, his base, who are decidedly "not acceptable" to the alt right becaise of their color or religion reconcile their status now?