The president and vice president of the United States campaign together and are elected as a team and not individually following the adoption of the 12th Amendment to the U.S. Constitution, which was drafted to prevent the nation's two highest elected officials from being from opposing political parties. The amendment made it more difficult, but not impossible, for voters to elect members of two political parties president and vice president.

Candidates for president and vice president have appeared together on the same ticket since the election of 1804, the year the 12th Amendment was ratified. Prior to the adoption of the constitutional amendment, the office of vice president was awarded to the presidential candidate who won the second-largest number of votes, regardless of which political party he represented. In the presidential election of 1796, for example, voters chose John Adams, a Federalist, to be president. Thomas Jefferson, a Democratic-Republican, was the runner-up in the vote count and thus became vice president to Adams.

How a President and Vice President Could Be From Different Parties

Still, there's nothing in the U.S. Constitution, particularly the 12th Amendment, that prevents a Republican from choosing a Democratic running mate or a Democrat from choosing a Green Party politician as her vice presidential candidate. In fact, one of the nation's modern-day presidential nominees came very close to selecting a running mate who wasn't from his own party. Still, it would be extremely difficult for a president to win an election in today’s hyperpartisan political climate with a running mate from an opposing party.

How could it happen? How could the United States end up with a Republican president and a Democratic vice president, or vice-versa? It's important to understand, first, that presidential and vice presidential candidates run together on the same ticket. Voters do not elect them separately but as a team. Voters choose presidents primarily based on their party affiliation, and their running mates typically are only minor factors in the decision-making process.

So, in theory, the most obvious way for there to be a president and vice president from opposing political parties is for them to run on the same ticket. What makes such a scenario unlikely, though, is the damage the candidate would sustain from members and voters of his party. Republican John McCain, for example, withered from the “outrage” of Christian conservatives when they found out he was leaning toward asking U.S. Sen. Joe Lieberman, a pro-abortion rights Democrat who left the party and became an independent.

There's one other way the U.S. could end up with a president and vice president could end up from opposing parties: in the case of an electoral tie where both presidential candidates receive fewer than the 270 electoral votes needed to win.

In that case, the House of Representatives would choose the president and the Senate would choose the vice president. If the chambers are controlled by different parties, they would likely pick two people from opposing parties to serve in the White House.

Why It's Unlikely the President and Vice President Would Be From Different Parties

Sidney M. Milkis and Michael Nelson, the authors of The American Presidency: Origins and Development, 1776–2014, describe a “new emphasis on loyalty and competence and the new care invested in the selection process” as a reason presidential nominees choose a running mate with similar positions from the same party.

“The modern era has been marked by an almost complete absence of ideologically opposed running mates, and those vice-presidential candidates who have differed on the issues with the head of the ticket have hastened to gloss over past disagreements and deny that any exist in the present.”

What the Constitution Says

Before the adoption of the 12th Amendment in 1804, voters chose presidents and vice presidents separately. When a president and vice president were from opposing parties, as Vice President Thomas Jefferson and President John Adams were in the late 1700s, many thought the split provided a system of checks and balances just within the executive branch.

According to the National Constitution Center, though:

"The presidential candidate who received the most electoral votes won the presidency; the runner-up became the vice president. In 1796, this meant that the president and the vice president were from different parties and had different political views, making governance more difficult. The adoption of Amendment XII solved this problem by allowing each party to nominate their team for president and vice president."

Support for Electing Presidents and Vice Presidents Separately

States could, in fact, allow separate votes for a president and vice president. But all of them now unify the two candidates on one ticket on their ballots.

Vikram David Amar, a law professor at the University of California at Davis, wrote:

“Why are voters denied the chance to vote for a president of one party and a vice president of the other? After all, voters often split their votes in other ways: between a president of one party and a House member or senator of the other; between federal representatives of one party and state representatives of the other.”