Florida Sen. Marco Rubio told ABC’s “This Week” that he believed he was ready to be president and would take an all-or-nothing approach to running if he does decide to go ahead, while also sounding skeptical notes on climate change and Hillary Clinton’s tenure as secretary of state — two likely hot issues in 2016.

Asked by Jonathan Karl if he thought he was ready, Mr. Rubio said quickly, “I do,” before adding some qualifiers.