Mitt Romney went on the attack in this week's Republican candidates' presidential debate.
And for the first time he set his sights firmly on rival Rick Santorum.
"I would personally like to see a different candidate enter the general election than any of the ones that remain in the contest. But realistically it takes quite a bit of time to actually build up a campaign .... And I think we're really to the point where that's just not an option any more and we are going to have to go to battle with the army that we have, not the army that we might want."
- Liz Mair, a former adviser on Rick Perry's presidential campaign
It is a sign of how seriously the Romney camp is now taking Santorum - who in recent weeks has emerged as his main challenger for the right to go up against Barack Obama in November.
In just a few days the Republican primary season kicks in again with votes in Arizona and Romney's home state, Michigan.
And according to the latest polls Michigan's voters have Romney and Santorum in a dead heat - leading to the possibility of a damaging defeat for Romney in a state he was once considered certain to win.
The failure of the former Massachusetts governor to really establish a clear lead in the Republican nomination race has left several senior figures in the party concerned.
Some are worried that the party is being diverted too much into internal squabbles, rather than reaching out to new and undecided voters.
And what was once thought unthinkable - a new candidate joining the primaries - could be openly debated, should Romney slip up in Michigan.
So, does the Republican race need a new candidate? Why has Romney been unable to sweep Republicans off their feet?
Joining Inside Story: US 2012 with Lisa Fletcher to discuss this are: Tom Redmond, a Republican consultant and supporter of Mitt Romney; Carrie Budoff Brown, a writer with Politico magazine; and Liz Mair, a former adviser on Rick Perry's presidential campaign.
|CAN A NEW CANDIDATE WIN?
› Under the rules, a candidate must win 1,144 delegates during the primary season to win a majority and secure the nomination
› It is thought that a new candidate jumping in now would only be able to compete in eight of the remaining primaries - that gives them a possible 519 delegates up for grabs
› But a good showing in those primaries could not only establish that candidate's credibility but also mean that none of the other candidates reach that 1,144 figure
› That would raise the prospect of what is known as a brokered convention, which essentially turns August's Republican convention into one big debate to decide the nominee