Last Friday, Rep. Paul Ryan looked like President Barack Obama’s new Republican best friend. The president showered praise on everything from his substantive budget proposal to his family during the now-legendary question-and-answer session with House Republicans.

 But rather than opening a hopeful new avenue for bipartisanship, the White House and Hill Democrats quickly went to work ripping apart Ryan’s “Roadmap for America’s Future” — which Obama himself said he had read.

 Democrats accused the Wisconsin Republican of trying to privatize Social Security, cut taxes for the rich and increase them for the middle class. Medicare would be allowed to “wither on the vine.” Here we go again, Rep. Xavier Becerra (D-Calif.) said Thursday of Ryan’s proposal. On Capitol Hill, Office of Management and Budget Director Peter Orszag deconstructed the plan, saying it would address long-term fiscal problems but in a way that many policymakers might find “objectionable” because it would shift risks and costs onto individuals and their families.

 In just a week, Ryan had gone from being seen as the smart conservative whom Obama might take seriously to being seen as the symbol of how Democrats believe Republicans would dismantle the social safety net if the GOP took control of Congress.

 Republicans believe the criticism was a setup....