Published: Mar 19, 2012 5:30 PM EDT

WASHINGTON (AP) - Rick Santorum is still promising to stay in the campaign for the long haul, even though he's virtually conceded that he can't earn enough delegates to win.
    
He told CBS' "This Morning" that he'll "go out and compete in every state," calling tomorrow's Illinois primary a "two-person race."
    
Santorum said it will be "very difficult" for any candidate to get enough delegates before the convention to clinch the nomination. He says he thinks the chances of a brokered GOP convention in August are "increasing."
    
Last night, Mitt Romney's wife Ann said the time has come for her husband's rivals to quit the race.
    
Romney -- who has said Santorum can't match him on economic expertise -- today referred to President Barack Obama as an "economic lightweight."
    
Santorum, on MSNBC this morning, called Romney as a "big-government heavyweight."
    
Romney's campaign is suggesting that tomorrow's primary in Illinois will extend Romney's delegate advantage, even if he loses the popular vote.
  
   
(Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)