But if the G.O.P. fully embraces the ideas its younger-generation leaders are pursuing, the Democrats could suddenly find themselves in a difficult spot. Liberals can theoretically outbid a limited-government populism, yes — but given the fiscal picture, they would need to raise taxes significantly to do so, alienating their own donors, the middle class or both. And the immediate liberal critique of Ryan’s new plan — that it’s too paternalistic, too focused on pushing welfare recipients to work — harkened back to debates that the Democratic Party used to lose.

Meanwhile, Obama-era liberalism has grown dangerously comfortable with big business-big government partnerships. It’s a bad sign when even the tribune of left-wing populism, Elizabeth Warren, feels obliged to defend, against libertarian populist attacks, an icon of crony capitalism like the Export-Import Bank.

So there’s a scenario — still unlikely, but much more plausible than a year ago — in which the pattern of 2012 could be reversed: A deepening association with big money and big business could suddenly become an albatross for Democrats, and the Republicans could finally — and deservedly — shake their identity as a party that cares only about the rich.