Greenville, South Carolina (CNN) It's a simple question, but one that stops Republican presidential hopefuls in their tracks: Who do you think is the greatest president alive today?

CNN posed the question to several White House contenders gathered here recently at the Freedom Summit, a daylong conference with conservative activists ahead of next year's primary in this crucial early-primary state.

"I'll leave that to the people to decide," said Texas Sen. Ted Cruz , which is his guaranteed go-to line for questions he doesn't want to answer. "Certainly the greatest president of recent generations was Ronald Reagan."

Ronald Reagan, as you might recall, has been dead for 11 years.

There are reasons why these White House hopefuls are suddenly shy when pressed on their thoughts about the five surviving presidents.

They can't say Jimmy Carte r, whose presidency is synonymous in GOP circles as weakness, or President Barack Obama, a man whose legacy they all have spent years trying to vanquish. Bill Clinton is a Democrat and the husband of Democratic presidential frontrunner Hillary Clinton -- so he's out.

That leaves the two Republicans: George H.W. Bush and George W. Bush, father and brother, respectively, of Jeb Bush, the former governor of Florida who is preparing his own bid for the Republican nomination. And an endorsement for a Bush could be construed as affirmation for Jeb Bush by proxy.

They also know that if you say George W. Bush is the greatest living president, well, then you're on camera saying you think George W. Bush is the greatest living president, and Democrats will have a field day. In 2008, GOP nominee John McCain didn't want to tie his campaign lasso to Bush, and neither do these contenders eight years later.

That might explain why former Texas Gov. Rick Perry ignored the question completely, walked away and hooted, "Bye y'aaaaall" on his way out.

Or why Ben Carson , the retired neurosurgeon, paused for several seconds before he just gave up. "I don't know," he said.

Former Pennsylvania Sen. Rick Santorum gets partial credit for threading the needle: "Probably a Bush," he said, and then escaped up a wheelchair ramp.

Well, at least almost everyone on the Republican campaign trail can agree: The late Ronald Reagan is America's greatest (previously) living president.