Santorum lays out a vision in which Romney is weakened by his failure in the first roll call and the party activists, preferring a more conservative candidate, begin migrating to Santorum.
"The problem with that in the practical sense is it would mean disenfranchising the majority of the Republican voters who voted in the primary process and picked Mitt Romney, to choose someone who got not only less delegates, but far less votes," said Steve Schmidt, who was senior adviser to John McCain's 2008 presidential campaign.
When delegates are unbound, there's no telling which way they'll turn or how long they'll take.
Democrats hold the record: 103 roll calls. That's how many votes it took to dismiss their two leading candidates and dozens of others in 1924 and settle on little-known West Virginia lawyer John Davis. He lost in a landslide to Republican President Calvin Coolidge.
In a more fortuitous choice, Abraham Lincoln came from behind to win the Republican nomination on the third roll call in 1860.
5. A brokered convention: The powerbrokers toss out the candidates and draft someone new.
It sounds crazy after decades of hermetically sealed conventions. And it's certainly a long shot. It would mean rejecting everyone who's received actual votes from the Republican faithful. But some delegates might see that as a more appealing way to compromise.
The last time one of the two major parties drafted its nominee — and the last convention to require more than one roll call — was when the Democrats turned to Adlai Stevenson in 1952.
The closed conclave of party elders who elevated Warren Harding to the front of the pack at the contentious 1920 Republican convention is believed to be the origin of the term "smoke-filled room."
The likeliest last-minute possibilities this year, such as New Jersey Gov. Chris Christie and Indiana Gov. Mitch Daniels, insist they don't want the call.
Former Florida Gov. Jeb Bush, whose name also has been bandied about, put the kibosh on the idea by announcing his endorsement. He said that "now is the time for Republicans to unite behind Gov. Romney."
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