WASHINGTON (AP) — Republicans considered to be up-and-comers are scrambling to declare a lack of interest in becoming Mitt Romney's running mate.With the former Massachusetts governor poised to win the GOP nomination in June, if not earlier, some of the focus has shifted to possible choices for the No. 2 spot on the ticket. But no one is rushing forward and many of the top prospects are trying to shut down the conversation before it begins.Florida Sen. Marco Rubio of Florida says it won't be him. South Carolina Gov. Nikki Haley says she'll say 'no' if Romney offers her the slot. Former Minnesota Gov. Tim Pawlenty says he took himself out of the running and New Mexico Gov. Susana Martinez also says she's not interested.