Both parties trace their lineage back to the founding of the United States in the late 1700s. By the mid-1800s, both had essentially become the parties known today.

In the 20th century, each party had a president who became an icon representing its principles.

Republican Ronald Reagan was elected in 1980. He promoted an agenda the party still follows, as the Republican National Committee's Sean Spicer explains.

"The Republican Party is the party of limited government, lower taxes, free enterprise, and generally supports a fairly conservative agenda," he said. 

The Democratic Party's iconic figure is Franklin D. Roosevelt. He became president in 1933, at the height of the Great Depression. FDR, as he was called, launched the "New Deal," with government-driven economic and social reforms to protect the working class. Melanie Roussell is the Democratic National Committee spokeswoman.

"Democrats have always tried to help working people establish the American dream by providing help to buy a home, to sending your kids to college, to helping the elderly - older people, seniors, to live a life that they can afford," said Melanie Roussell, the Democratic National Committee spokeswoman. "It's really about government working with people."

The two parties appeal to different social, demographic, and even ethnic groups. Democrat Roussell says her party's following today reflects Franklin Roosevelt's focus.

"Our core constituent groups, I would say, are young Americans, women, African Americans, Hispanic voters," she said. "Again, we are the party of inclusion." 

The Republican Party's support includes tradition-oriented, white voters with conservative Christian religous views. 

While the party has been the long-time choice of the upper classes, Ronald Reagan, and an earlier Republican president, Richard Nixon, attracted working-class voters who had traditionally supported the Democrats. And spokesman Sean Spicer says in the 1990s the Republicans saw a number of shifts, bringing voters in new areas. 

"We started to see a bit of a transition where the Republican Party grew a lot more in the South, and ebbed a little in the Northeast," he said. "Now, what you are seeing is a lot more of the party trying to push out into the Midwest, to grow stronger in places like New Mexico and Colorado, Nevada, where we are seeing a lot of the party's growth. 

The current president, Barack Obama, is a Democratic. His predecessor, President George W. Bush, is a Republican.