On a recent morning on Manhattan’s Upper East Side, Alan Patricof, one of the pioneers of private equity, was wedged into a booth at the Three Guys diner, mulling an investment that did not pan out.

His investment was not a flashy technology start-up or a leveraged buyout. It was Senator Hillary Rodham Clinton. A staunch Clinton supporter since the early 1990s, Mr Patricof served as one of the former First Lady’s national finance chairmen, helping to raise hundreds of millions of dollars for her failed White House bid.