PHILADELPHIA — It was a tough spot for Tim Kaine: sandwiched between Joe Biden, the party’s beloved vice president, and President Barack Obama, still wildly popular among Democrats, both delivering their final convention speeches after 8 years in office.But Tim Kaine was “listo” -- ready -- for his turn in the spotlight.He was stiffer than in his more raucous debut in Miami four days ago and the strategic bits of Spanish didn’t resonate as well.