By Larry Kane

PHILADELPHIA (CBS) — From Maryland to Wisconsin, Mitt Romney scored impressive primary wins on Tuesday night, but Rick Santorum says there’s another half left.

Romney easily won in both Maryland and Washington D.C., but in the key state of Wisconsin, it was a more narrow victory for the former Massachusetts governor.

But the win was big.

Wisconson is a battleground state — and so is Pennsylvania.

Rick Santorum says its only halftime. But halftime for which candidate?

Romney has more than half of the delegates needed to win the nomination, a commanding lead over Santorum, yet Santorum is campaigning in Pennsylvania for the Primary in 20 days — and he’s hoping to hold on for Texas in late May.

When you look at the map, Pennsylvania, Texas, and Nebraska may be Santorum’s only hope.

With pressure on him to quit, Santorum also has to notice the news that the Republican National Committee is now working to jointly do fund raising with Romney.