Identity politics is often a winner, and Mr. Santorum does it well. If only he could stop at identifying with this audience, rather than feeling the need to give them special favors.

As he explained this week, he doesn’t agree with the Democrats who are about “raising taxes” and “increasing dependency.” Yet he also doesn’t agree with Republicans who say “let’s just cut taxes, let’s just reduce spending, and everything will be fine.” Rather, he believes his job is to “look at those who are not doing well in our society.”

And so at the heart of the Santorum agenda are policies designed to give special handouts to the working class, simply because they are the working class—and even then only to segments of this group. That’s behind Mr. Santorum’s zero corporate tax on manufacturers, which benefits only Americans working in manufacturing. (Job at Wal-Mart? No soup for you!) It’s behind his plan to triple the child tax credit, which benefits only Americans fortunate enough to have a child. (Stalled love life? No soup for you, either!) Call it preferential populism…

In an election that needs to be about contrasts, this is point Obama. Game on for candidate Santorum, who gets to explain why his own policies for government to reward certain classes of citizens over others are any different than Mr. Obama’s. Or let’s see candidate Romney knock Mr. Obama’s proposals to further tax America’s job creators, those Mr. Romney thinks are doing “just fine.” The bigger risk is that a Republican president actually pursues these distorting economic policies, sacrificing growth.