(Of the deep cuts the Ryan budget makes in order to bring the budget into balance, only a small fraction could be offset by repealing George W. Bush’s tax cuts for the rich, the usual liberal answer to deficit reduction.)It is true that liberals like to talk a lot about taxes on rich people, probably because it's the most popular deficit-cutting option out there.
But depending on which liberals you're talking about, there's no shortage of any "liberal answer to deficit reduction." It's just that in the war on budgeting precincts that Douthat hangs out in, they don't count.
To begin with: most liberals, including Barack Obama, want significantly lower levels of military spending than, say, Mitt Romney wants. There's a lot of money in that pot!
Second, there's another fairly big pot of stuff that various different liberals are either happy or at least willing to cut from current spending: farm programs, various business subsidies, things like that. Some of them are popular, and so liberals don't want to talk about it up front, but they do support them.
Third? How about that $700B plus chunk that the ACA took out of Medicare? Okay, it's fair to point out that the Medicare cuts and the new taxes in health care reform pay for new spending in ACA. Still, worth mentioning, particularly in comparison to Medicare Part D.
And, fourth, all of the other cost-cutting measures in health care reform. Will those things work? We don't know! But they are real efforts at deficit reduction (above and beyond the cost offsets), and Democrats, liberal or not, were willing to vote for them even though they weren't very popular.
Again, it's tricky to deal with this because different liberals have different preferences, but it's almost always true that for example the Progressive Caucus budget in the House has a lower long-term budget deficit than either the Democratic or Republican budgets.
I'm going to leave the rest of Douthat's piece alone...I basically don't agree with him that Paul Ryan has been a very responsible bipartisan budget-balancer who just has been forced by circumstances to act as if he was an irresponsible math-defying partisan ideologue, but what are you going to do. But I suppose that there's perhaps enough ambiguity there that multiple interpretations are plausible. But the truth is that Democrats, including and perhaps even especially liberal Democrats, have proposed and when they had the chance enacted lots of real, specific, deficit-reducing things over the last thirty years, and Douthat is wrong to ignore them.