As Ross Douthat, the Times’ resident reformicon, acknowledged, the GOP base considers refundable tax credits of any sort to already be a centrist compromise. These are the people who think that poor people are poor because of their own failings and that they’re being coddled by the social safety net. That’s why Mitt Romney’s infamous “47 percent” comment resonated with Republicans, and why it spells doom for the reformicons: 47 percent of Americans pay no income tax precisely because of the sort of tax breaks for workers and families reformicons want to utilize.
Look at it this way: even Salam’s idea of “progressivity-neutral” tax reform constitutes the far left edge of what the GOP’s coalition of voters and interests will tolerate, after you’ve overcome all their natural instincts and interests.
The Democratic Party, by contrast, is already on the record supporting increases in the EITC and the CTC. Their voters do not think the poor are their own worst enemy, or that they’re coddled by government. They will be friendlier to the multiple different ways of paying for the credits. In short, the Democrats’ coalition provides the reformicons with a menu of different possible policy alliances and compromises that the GOP simply does not.