Some Republicans are outraged and think that Mr Gingrich has made a big mistake.
It certainly felt too small after his Myrtle Beach success to accommodate Mr Gingrich's gargantuan self-belief.
Mr Gingrich supports a flat tax and has denounced Mr Romney's plan as Obama-style class warfare.
Fox this week suspended Mr Gingrich and Mr Santorum, pending clarification of their plans.
How did Mr Gingrich, with less money and a smaller organisation, turn the tide so quickly?
Compared with Mr Gingrich, he was less given to extreme remarks, less grandiose, less pot-bellied.
There is, however, another way in which Mr Gingrich's high standing in the polls is improbable.
ECONOMIST: After Mr Dopey and Mr (too) Friendly, Mr Grumpy gets his turn
On the face of things, Mr Gingrich makes an unlikely champion for the Republican right.
But both Mr Brooks's subtle approach and Mr Gingrich's unsubtle one suffer from a shared weakness.
Mr Gingrich's attacks have not stopped Mr Romney surging ahead, and that may tell you something.
Mr Gingrich's team vowed to pursue an "aggressive write-in campaign" - although Virginia does not permit this.
Mr Santorum came in second with 31%, with Mr Gingrich and Mr Paul on 15% and 12% respectively.
In fact, of course, Mr Boehner cannot dream of controlling the House Republicans the way Mr Gingrich did.
Most of Mr Gingrich's article was a disquisition on the dangers inherent in forming a common European currency.
Mr. Gingrich's lawyers said they relied on Mr. Gingrich and his staff to ensure that the letters were accurate.
Mr Santorum and Mr Gingrich both had only limited campaign activity in Maine.
Mr Gingrich, a walking, talking, and sometimes dangerously undisciplined ideological fireworks display, was a different species of politician altogether.
No charge that grave is laid against the far less likeable Mr Gingrich.
ECONOMIST: After Mr Dopey and Mr (too) Friendly, Mr Grumpy gets his turn
He has spent barely two weeks in Iowa this year, compared with Mr Santorum's 14 and Mr Gingrich's eight.
Mr Romney also won resoundingly in Virginia, where Mr Santorum and Mr Gingrich failed to qualify for the ballot.
This happened with Ronald Reagan in the late 1970s and then again, rather less triumphantly, with Mr Gingrich in 1994.
Republicans in Washington are increasingly agitated that they cannot attempt to repeal affirmative action with Mr Gingrich at the helm.
When asked about his moral underpinnings, Mr Gingrich says that it is impossible to find fulfilment without submitting to God's mercy.
In return, Mr Romney has mounted a blitzkrieg against Mr Gingrich, much of it focused on his political and personal integrity.
The closest thing to a knife fight has been Mr Gingrich's portrayal of Mr Romney as a callous wrecker of humble livelihoods.
Mr Gingrich faces his home state primary, in Georgia, on Super Tuesday.
In a profession which specialises in hypocrisy, Mr Gingrich's performance stands out.
The letter was signed by Mr. Gingrich's attorney, but Mr. Gingrich reviewed it and approved it prior to its being delivered to the committee.
It is bad luck for Mr Gingrich that one of his former wives has been so willing to disparage his fitness for the presidency.
ECONOMIST: After Mr Dopey and Mr (too) Friendly, Mr Grumpy gets his turn
That money was chiefly spent bashing Mr Romney, who promptly began to slide in the polls, paving the way for Mr Gingrich's subsequent victory.
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