Representative Paul D. Ryan of Wisconsin, the chairman of the House Budget Committee and a favorite of many fiscal conservatives, takes his turn on Monday when he welcomes Mr. Romney to his hometown, Janesville. The list is also thought to include at least two governors, Chris Christie of New Jersey and Bobby Jindal of Louisiana, and two senators, John Thune of South Dakota and Marco Rubio of Florida…

The selection is still done with intense secrecy, but the Romney campaign has intentionally sought to eliminate at least some of the mystery about who might run. The back-to-back tryouts, first with Mr. Pawlenty, and then with Mr. Portman flipping pancakes with Mr. Romney on Sunday and standing alongside him for much of the day, provided a chance for the campaign to assess how Mr. Romney and either of the two would look as a ticket.

In the privacy of Mr. Romney’s bus, the two chatted about politics and policy as they chugged across Ohio. Mr. Portman even helped clean up some of Mr. Romney’s grandchildren, who were out on the road for the day and messy from blueberry pie…

Mr. Romney and his aides have carefully studied other vice-presidential selections — Democratic and Republican ones — and concluded that a do-no-harm approach best fits this election.