With those battle lines drawn, the candidates turn to special interest groups and independent voters, hoping to win on the margins in what is shaping up to be a narrow election on Nov. 6.
The Democratic National Convention kicked off Tuesday with a full-throated appeal to Latino and women voters. Larry Sabato, director of the Center for Politics at the University of Virginia, said Obama will need both groups to hang onto the White House.
"It he slips a little bit with either group, he's finished," Sabato said. "And they know it. This is an election on the margin."
Tim Malloy, assistant director of the Quinnipiac University Poll, said just 4 to 6 percent of voters in swing states are undecided.
"It seems like most people have decided," Malloy said.
The Democrats seemed confident on their first day in Charlotte, N.C. Newark Mayor Cory Booker fired off a rousing speech for the normally bureaucratic introduction of the party platform.
Booker called the platform a choice of pragmatism over partisanship. He railed against "a country of savage disparities that favor fortunate few over the greatest driving force of any economy, a large and robust middle class."
First lady Michelle Obama did not mention Romney. She used the first night of the convention to talk about how Americans inspire her, including a soldier blinded by a bomb in Afghanistan.
That was likely to draw comparisons, since Romney chose not to mention that war during his convention speech last week.
Obama described growing up like her husband in families with little to spare but unconditional love and a thirst for education.
Obama said she didn't want the presidency to change her husband, to alter the way he was taught to respect everyone.
She added, "I have seen firsthand that being president doesn't change who you are. It reveals who you are."
Obama touted the Affordable Care Act, also known as Obamacare, repeating her often used line that people should not go broke due to an illness or accident.
Obama took on a common GOP jab at her husband, that he started as a community organizer. She said he passed up high-paying jobs to take on that work.
"For Barack, success isn't about how much money you make," she said. "It's about the difference you make in people's lives."
The resounding theme Tuesday was "Mitt Romney doesn't get it." The hardest jabs came from former Ohio Gov. Ted Strickland, Mass. Gov. Deval Patrick and keynote speaker Julian Castro, mayor of San Antonio, Texas.
Strickland pummeled Romney for his overseas bank accounts, claiming he has "so little economic patriotism that even his money needs a passport."
Patrick spoke of following Romney in the Governor's Office, finding deep cuts to education, crumbling infrastructure and a state ranked 47th in job creation.
"He's a fine fellow and a great salesman, but as governor he was more interested in having the job than doing it," Patrick said.
Castro was introduced by his twin brother Joaquin, who is favored to win in November a Texas seat in the U.S. House.
Julian Castro cast their political rise as an "unlikely journey" possible only in America.
He was less impressed by what he called "a few stories of individual success" cited at last week's Republican National Convention.
Castro said Romney's budget plans, tax cuts and reduced federal spending to spur growth, would dismantle the middle class. He noted that those plans were previously called "trickle-down" and "supply-side" economics.
"Either way, their theory has been tested," Castro said. "It failed. "Our economy failed. The middle class paid a price."
Contact Chris Brennan at firstname.lastname@example.org or 215-854-5973. Follow him on Twitter @ChrisBrennanDN. Read his blog at www.PhillyClout.com.