COLUMBUS, Ohio — Mitt Romney is savoring the energy surrounding his candidacy, talking with rising confidence about his ability to overtake President Obama in the closing days of the race.

He dwells far less on the biggest obstacle facing his campaign: the Electoral College.

A decade after taking the first steps in his quest to win the White House, Mr. Romney can finally see the presidency within his grasp, his advisers say. To many Republicans, he sounds more presidential than at any other moment of his campaign, a point that was not lost on his audience Wednesday in Nevada, when he declared: “If I’m elected — no, when I’m elected.”

But the swelling crowds and the fresh optimism among his supporters do not minimize the challenge confronting him across a wide landscape of battleground states, where Mr. Romney must win a series of individual statewide races, rather than a national contest. His room for error is so slight, one adviser said, the mathematics could be more daunting than the politics.

The enthusiasm gathering around Mr. Romney came into view on Wednesday as he traveled through Colorado, Nevada and Iowa, appearing before thousands of supporters as he fought to keep alive the sense that he had gained stature and credibility as an alternative to Mr. Obama at the debates and was on an upward trajectory.