I don’t know what “fitness to be President” means. Certainly, I have argued that the current occupant at 1600 Pennsylvania Avenue is unfit for the office (and I am not resorting to Constitutional questions).
Mr Gingrich was magnificient as an opposition leader when the Republicans were in the minority in the House of Representative, and I give him great credit for the results of the 1994 election.
However, when Speaker of the House, he reportedly would have a grand idea on a daily basis which then was the top priority. The next day, he would have a new grand idea which became the new top priority.
I think that the president needs to be a little more focused. I think highly of Mr Gingrich, but I shudder at the thought of him as president of the Republic.
In short, he must be an arrogant elitist with Marxist tendencies... according to any lib you would talk to.