The problem, these purveyors of the conventional wisdom all said, was Medicare -- to be more specific, the future changes in Medicare set out in the budget resolutions Ryan fashioned as House Budget Committee chairman and persuaded almost all House and Senate Republicans to vote for.
But while Democrats licked their chops at the prospect of scaring old ladies that they'd be sent downhill in wheelchairs, the Medicare issue seems to be working in the other direction.
Romney and Ryan have gone on the offense, noting that while their plan calls for no changes for current Medicare recipients and those over 55, Obamacare, saved from demolition by Chief Justice John Roberts, cuts $716 billion from the politically popular Medicare to pay for Obama's politically unpopular health care law.
The Romney campaign is putting TV advertising money behind this message, and it will have plenty more to spend -- quite possibly more than the Obama forces -- once the Romney-Ryan ticket is officially nominated in Tampa, Fla., in 10 days. Team Obama is visibly squirming.
It turns out that Ryan and Romney, who in late 2011 and early 2012 moved quietly but deliberately toward embracing the Ryan agenda, may have outthought their adversaries.
Those last-minute Mediscare-type mailings to seniors, which enabled Democratic Gov. Lawton Chiles to narrowly defeat Jeb Bush in the 1994 Florida governor race, don't work so well anymore when the issue is brought out fully in the light of day.
But Medicare/Mediscare is not the only thing on which the Democrats have underestimated Ryan and the putative presidential nominee who selected him from the high-quality field of potential VP nominees from which he made his pick.
Ryan brings two other things to the Republican ticket that could prove important in the two-month sprint from the Tampa and Charlotte, N.C, conventions to Election Day.
One is foreign policy chops. Romney has less in the way of exposure to serious involvement in foreign and defense policy than any major party nominee since Bill Clinton in 1992 and Romney's fellow Bay Stater Michael Dukakis in 1988.
Ryan, as a member of the House, theoretically brings a little more. But actually a good bit more, to judge from a little noticed speech he delivered three blocks from the White House to the Alexander Hamilton Society in June 2011.
In that speech, as Wall Street Journal columnist Bret Stephens noted last week, Ryan showed that "he knows how to think."