Presidential nomination debates are supposed to separate the sheep from the goats and finally identify the party's best candidate to run in the general election in the fall. But after 20 or more such talkathons this season, the Republican Partyremains pretty much leaderless.

Wednesday night's debate in Mesa, Ariz., among the four surviving GOP aspirants demonstrated as much as anything that their party continues to struggle to find not only that candidate, but also a persuasive message for electing any of them.

They continue to argue that President Barack Obama's stewardship of the national economy is their sure ticket to ousting him. But some signs of recovery in a reawakening stock market and a slowly dropping unemployment rate now hamper that Republican pitch. Mitt Romney, especially, clings to it in his self-salesmanship as a corporate turnaround magician who can do the same for the whole country.

The emergence of Rick Santorum as the latest anti-Romney, mostly thanks to the implosion of other interim front-runners, has in recent weeks diverted the party into the political dead end of culture war. His rigid and insistent injection of religion into the debate has put him on the defensive and extended the Republican circular firing squad that the debates have become.

In Mesa, Mr. Romney hammered Mr. Santorum again on his devotion as a senator to legislative earmarks beneficial to his state of Pennslvania, arguing that his resort to them was a mockery of his declared pursuit of a smaller federal government. Mr. Santorum hit back by noting Mr. Romney's own tapping of federal taxpayers' money to save the faltering Winter Olympics in Utah in 2002.

They also sparred over the 2008 federal bailouts of Wall Street banks and the Michigan-centered auto industry, both of which Mr. Santorum opposed. He noted Mr. Romney's support of the first and his conspicuous opposition to the second in his native state, which holds its Republican primary on Tuesday, along with Arizona.

Mr. Romney defended the bank bailout as imperative to avoid collapse of the whole banking system. He said he favored the managed bankruptcy and reorganization of the car companies that finally turned them around in the first years of the Obama administration.

In all this, the other two candidates, former House Speaker Newt Gingrich andRep. Ron Paul of Texas, were essentially reduced to kibitzers in the exchanges. Mr. Paul defended his accusation of Mr. Santorum as "a fake" consistent conservative, citing his call for repeal of the No Child Left Behind education bill he once voted for. Mr. Santorum acknowledged he had been wrong the first time.

Mr. Gingrich, struggling to regain his footing after once leading the pack in the polls, showed a relatively benign face. He agreed with Mr. Romney that managed bankruptcy by the auto companies was preferable to the federal bailout, which he said benefited and strengthened the hand of the United Auto Workers. He seemed for once focused on countering his usual confrontational image.

None of this two-hour chatter materially altered the picture of the Republican contest, other than perhaps being a missed opportunity for Mr. Santorum to elevate his image as a credible aspirant for the presidency beyond being the last man standing with the amiable but tenacious Mr. Romney.

With Mr. Romney favored to win in Arizona on Tuesday, the Michigan primary is likely to be Mr. Santorum's best chance to trip him up. Doing so would only reinforce the notion that the Republican Party has yet to find either the man or the message with which to deny Mr. Obama a second term.

If Mr. Romney in his native state can survive Mr. Santorum's challenge, he may at least stem the recent musings that lack of enthusiasm for him, coupled with the intentions of Mr. Paul and Mr. Gingrich to go all the way to the party convention, could produce a late entry's nomination there.

However, with the economy showing some signs of resuscitation, in November Mr. Romney or any other nominee will likely need a more persuasive argument to voters than simply being the non-Obama. Banking on worse times is no worthy formula, either, for returning a Republican to the White House.

Jules Witcover's latest book is "Joe Biden: A Life of Trial and Redemption" (William Morrow). His email is juleswitcover@comcast.net.