Renaissance Technologies, a hedge fund founded by billionaire James Simons, donated over $13 million to Sen. Ted Cruz’s failed presidential campaign. For a guy who’s supposed to be pretty smart with his money, the ROI on that one has got to sting. Nevertheless, now that Mr. Cruz is out of the race, Mr. Simons has begun pouring millions of dollars into Hillary Clinton‘s campaign, with Renaissance Technologies donating over $2 million to Ms. Clinton so far this election cycle. Euclidean Capital—also owned by Mr. Simons—has given the Clinton campaign over $7 million in contributions, and such figures are likely to...