Our guess is that most Yale University professors are proud to be progressives. Well, they are now getting the chance to live their convictions as Connecticut Democrats attempt to soak Yale’s rich endowment.

Facing a $220 million budget shortfall, Democrats in Hartford have proposed taxing the unspent earnings of university endowments with more than $10 billion in assets. Only Yale’s $25.6 billion endowment—the country’s second largest after Harvard—fits the tax bill. Yale’s tax-exempt investments earned $2.6 billion last...