The Democratic 2020 primary is a crowded field, but regardless of who takes the nomination, President Donald Trump will face a battle before election day.
Those running a primary campaign against a sitting president have little chance of success—the only elected president to lose his bid for a second term in the following primary was Franklin Pierce in 1857, according to NPR—but that doesn't mean their campaigns won't have an impact.
Presidents who face a reputable challenge in the primary frequently lose reelection, even after winning their party's nomination; a divided party is less likely to turn out the votes needed. The last time this happened was in 1992, when President George H. W. Bush lost reelection to Bill Clinton after facing a far-right candidate in the primary.
These are the Republicans who are likely hoping against the odds to go somewhere in the 2020 primary.
Mark Sanford, the former South Carolina governor and congressman, has decided to launch a longshot Republican challenge to President Donald Trump.
"I am here to tell you now that I am going to get in," Sanford said in an interview on "Fox News Sunday."
When asked why he was taking on an incumbent who's popular within the party, Sanford said: "I think we need to have a conversation on what it means to be a Republican. I think that as the Republican Party, we have lost our way."
The 59-year-old Sanford has long been an outspoken critic of Trump's. He frequently questioned Trump's motivations and qualifications during the run-up to the 2016 presidential election and called Trump's candidacy "a particularly tough pill to swallow." —Associated Press
Weld announced his candidacy for president on April 15. His campaign launch video touts his successes after becoming the first Republican governor of Massachusetts in nearly 20 years in 1991, a win that rebooted a conservative trend in the majority blue state (since he left office in 1997, only one Democrat has sat beneath Boston state house's golden dome). As governor, Weld says he cut taxes 21 times, balanced the state budget, and instituted work requirements in the welfare system.
While he's economically conservative, Weld supports abortion rights, same-sex marriage, and climate change action—all traditionally liberal positions that could distance him from Trump's base. On healthcare, Weld opts to reform the Affordable Care Act to provide a free market with more choices.
He may also face criticism for a lack of party loyalty. While Weld maintains that his beliefs never changed, he ran on the 2016 Libertarian ticket as Gary Johnson's vice president. In 2008, he endorsed Democratic candidate Barack Obama for president over his party's John McCain. Four years later, he reversed again to endorse Mitt Romney over Obama.
Moreover, Weld has long been a critic of Trump. During the 2016 election, he likened Trump's immigration policy to Nazi Germany. He also told CNN at the time that he didn't believe Trump has "the temperament or the stability" to be president. More recently, he told Rolling Stone that the president is a "malignant narcissist" that's "kind of like that crazy clown in A Clockwork Orange."
This sentiment has carried into Weld's campaign: his launch video, more than three minutes long, dedicates a sizable portion to clips of Trump's most controversial moments. He shows Trump's support of "both sides" after the deadly Charlottesville protests, his friendliness towards Russian President Vladimir Putin, the infamous Access Hollywood tape where Trump admits to sexually assaulting a woman, and more.
With his bid for presidency, Weld is offering "a better America." Even if he can't win the primary, Weld told Rolling Stone he'd "be flattered to be Kennedy to [Trump's] Carter," referring to the 1980 election where Sen. Ted Kennedy ran a primary campaign against President Jimmy Carter, leading the incumbent to lose the White House to Ronald Reagan.
After running a failed presidential primary campaign in 2016, former Ohio governor Kasich is considering another bid. He has yet to officially announce his candidacy, but hasn't ruled it out either.
Kasich's record is traditionally Republican in many ways: he defunded Planned Parenthood in Ohio, advocates for lower taxes, and supports the Keystone pipeline (although he says climate change is a real threat, a reversal from his 2016 stance). He also wants to revise the Affordable Care Act and expand Medicaid. In terms of same-sex marriage, Kasich says he accepts the Supreme Court's ruling.
Like Weld, Kasich also has a few beliefs that lean moderate. He supports Dreamers (those who were brought to the U.S. illegally as children) and the issues surrounding Black Lives Matter. While he wants to protect the Second Amendment, Kasich has also advocated for background checks and increased attention to mental illness.
Kasich told the Associated Press that he supports Trump's moves towards increased border control, lower taxes, and greater financial contributions from European allies, but in many other ways he disagrees with the sitting president.
"Tariffs are a bad idea. Debt is a bad idea. Family separation is a bad idea. Demonizing immigrants is a bad idea. And breaking down our alliances is bad too," Kasich told the AP in December.
Joe Walsh, a former Illinois congressman, says he'll challenge President Donald Trump for the Republican nomination in 2020. The tea party favorite argues that Trump is unfit for the White House.
Walsh announced his candidacy during an interview on ABC's "This Week'" on Sunday. Also in the race is Bill Weld, a former Massachusetts governor.
Walsh won a House seat from suburban Chicago in the 2010 tea party wave, but lost reelection in 2012 and has since hosted a radio talk show.
He has a history of inflammatory statements regarding Muslims and others, and said just before the 2016 election that if Trump lost, "I'm grabbing my musket." Walsh has since soured on Trump.
“If Republicans don’t stand up right now and challenge this guy right now — he’s bad for the party, he’s bad for the country — we’re going to get wiped out in 2020,” Walsh told CNN. —Associated Press
More must-read stories from Fortune:
—Will gaffes hurt Biden’s chances of a 2020 win? Strategists are divided
—These are the 2020 senate races to watch
—What is BDS? Boycott, Divestment, and Sanctions explained
—When does Congress reconvene? August recess, explained
—Trump thinks he is winning the trade war, but the data tell a different story
Get up to speed on your morning commute with Fortune’s CEO Daily newsletter.