In public, Rick Santorum brushes off the messages from party leaders and rising numbers of conservative voters that the Republican race is all but over, that his campaign has entered its end game.

But advisers to Mr. Santorum acknowledged on Wednesday that the road ahead is much steeper and more potholed now after Mitt Romney’s three-primary sweep on Tuesday.

More significant than the delegates that Mr. Romney accrued this week are the warnings flashing “Danger” in voter surveys that some of Mr. Santorum’s conservative base may be turning away.