(Reuters) - The nominating contest for the 2020 U.S. presidential election will kick off Feb. 3 with the first-in-the-nation caucuses in Iowa.

FILE PHOTO: Seven of the Democratic US Presidential candidates including former U.S. Vice President Joe Biden, Sen. Amy Klobuchar, Sen. Elizabeth Warren and Sen. Bernie Sanders, walk arm-in-arm with local African-American leaders during the Martin Luther King Jr. (MLK) Day Parade in Columbia, South Carolina, U.S. January 20, 2020. REUTERS/Randall Hill/File Photo

A dozen Democrats are vying to challenge Republican President Donald Trump in the November 2020 election, while three Republicans have mounted primary challenges against Trump. The Republican primary, even though votes will be held in some states, is a forgone conclusion as no challenger to Trump has gained any traction.

Here are the key dates on the election calendar in 2020:

Feb. 3: Iowa caucuses. Unlike a primary election, which is similar to a general election, Iowans gather in school gyms, living rooms and other community centers around the state to cast their votes publicly. Instead of paper ballots, Democrats sit or stand together in groups to show their support for candidates. The results of the nation’s first caucuses often have an outsized effect on the contest, setting the tone for the rest of the primary.

Feb. 7: Eighth Democratic primary debate in New Hampshire.

Feb. 11: New Hampshire primary. The results of the nation’s first primary historically has narrowed the field of candidates to a handful who compete for the nomination.

Feb. 19: Ninth Democratic primary debate in Nevada.

Feb. 22: Nevada caucuses. The outcome in the western state, which employs a caucus rather than a primary, could turn on the Latino vote, with Latinos accounting for 28% of the state’s population.

Feb. 25: Tenth Democratic primary debate in South Carolina.

Feb. 29: South Carolina primary. The southern state is a crucial early test for Democratic candidates’ strength among black voters, who make up two-thirds of the state’s primary electorate.

March 3: California, Texas and 12 other states hold primaries. Know as “Super Tuesday,” it could be a make-or-break day, with an enormous haul of delegates available for the taking.

March-June: More nominating contests are held in other states, Puerto Rico, Washington, D.C., and overseas territories. During that time, two more debates are scheduled to occur, one in March and one in April.

July 13-16: Democratic National Convention in Milwaukee, the largest city in Wisconsin. The state’s swing to Trump in 2016 was key to his victory.

Aug. 24-27: Republican National Convention in Charlotte, North Carolina. Like Wisconsin, North Carolina narrowly supported Trump in 2016 after having voted Democratic in the previous two presidential races.

Sept. 29: First presidential debate in Indiana.

Oct. 7: Vice presidential debate in Utah.

Oct. 15: Second presidential debate in Michigan.

Oct. 22: Third presidential debate in Tennessee.

Nov. 3: Election Day