But people who want him to run for president have already donated $12 million to the cause. A look at whom those donors also backed suggests that his support isn’t relegated to the fringe of the Republican Party, although the donors have given more to Tea Party and insurgent Republican groups than to party committees.

The amount of money raised so far is enough to show that there is interest in a candidacy by Mr. Carson, a frequent Fox News commentator with a biography that any candidate would envy. Raised by a single mother, he graduated from Yale and rose to prominence as a surgeon at Johns Hopkins. His speech to the 2013 National Prayer Breakfast gained him many fans among critics of President Obama.

Presuming that most of the people who donated to his committee would also support a presidential campaign with their money, a campaign by Mr. Carson would be able to raise enough money to contest one or more of the early Republican primaries or caucuses.