Mitt Romney bucks his party. Republicans should follow his leadership.

On Sunday, Romney and Sen. Michael F. Bennet (D-Colo.) unveiled a promising bipartisan proposal that would expand the child tax credit. But more than that, it potentially signals a coming Republican Party realignment over the federal government’s obligations to families. That’s because Romney is the first GOP lawmaker ever to endorse what’s known as a “fully refundable” child tax credit, according to Joshua McCabe, an Endicott College professor and author of a book on the politics of the child tax credit.

The Bennet-Romney proposal expands the child tax credit in two key ways. First, it makes the existing credit more generous to families with children under age 6 by raising its maximum value to $2,500 (vs. $2,000 available under current law).

Additionally, and perhaps more historically significant: The proposal would for the first time ever extend the child tax credit to the very poorest children by making the first chunk of the credit available to families regardless of income. That is, families with kids might have very low or even zero earnings (think: a single mom working toward a degree, say, or a retired couple raising their grandchildren) and still get a significant check.