Sen. Bernie Sanders, I-Vermont, appeared on CNN recently and accused Donald Trump and “others” of racism. The stated reason for this accusation is that Trump and other Republicans are trying to delegitimize President Obama and his presidency. The actual reason is a little more complicated than that.

Hillary Clinton, Sanders’ rival for the Democratic nomination, has been edging out Sanders since New Hampshire by appealing to the African American community and by suggesting that Sanders is less than loyal to President Obama. Clinton appears to be headed to a convincing win in South Carolina as a result. Sanders is attempting to signal that he too is loyal to America’s first black president, something of concern in the African American community where Obama still enjoys some popularity.

The other reason Sanders made the racism charge is because he is trying out a general election strategy, which is to paint any Republican candidate as racist for opposing President Obama. Republicans have opposed most things the president proposed, from Obamacare to closing Gitmo, to recommending a liberal replacement for Supreme Court Justice Antonin Scalia. Republicans are opposing Obama on policy and ideological grounds. Whoever is nominated on the Democratic ticket will be sure the stir up racial paranoia instead.

Trump is especially vulnerable to the charge of racism. He has said politically incorrect things about Mexicans and Muslims. Before he was a candidate, he plunged into the birther fever swamp by claiming that President Obama was born in Kenya and not, at the record shows, Hawaii.

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The idea was that if Obama was born in Kenya, he would not be eligible for president, something that most constitutional lawyers dispute since the president’s mother was an American citizen. Trump has been using the same tactic to try to cast doubt on Ted Cruz’s eligibility to be president, since the Texas senator was born in Canada.

The idea that Trump could be the Republican presidential candidate has many Republicans nervous, not the least because he is open to the sort of charges that Sanders has levied. It should be noted, though, that Trump won 46 percent of the Hispanic vote in Nevada, despite his hard line on illegal immigration. Democratic attacks on Trump may not work anymore than Republican attacks have.