Given President Donald Trump‘s controversy-plagued tenure in office thus far, there has been much speculation for some time — especially since the midterm elections ended — about which Democrats might run against him in 2020.

Even Republicans have said at least one person in the party’s ranks should challenge Trump, even potentially as an Independent candidate. Ohio Gov. John Kasicha failed GOP presidential contender in 2016, has been floated as a possible challenger.

In an interview on Fox News on Thursday, Trump was asked how he would feel if Kasich or retiring Republican Sen. Jeff Flake of Arizona — another of the president’s critics but also a supporter of Trump in some respects, like the Brett Kavanaugh vote — ran against him in 2020.

“I hope so,” the president responded.”

Kasich told ABC’s George Stephanopoulos last month he was “very seriously” thinking about running in 2020, while Flake said he hadn’t “ruled it out” yet and added he considers Kasich is a viable candidate to oppose Trump.

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With all this in mind, let’s take a look at some of the top potential Democratic challengers to Trump in 2020, including the top ten contenders:

  1. Joe Biden

Perhaps one of the most qualified candidates to run for president in 2020 — or at least that’s what the former vice president recently said about himself — Biden has been one of Trump’s fiercest critics and appears to be well-liked by a large proportion of Democrats. Like the current president, Biden is known for sometimes having a big mouth (although he arguably has more of a filter than Trump) but has also demonstrated his ability to connect with many different types of voters.

2. Bernie Sanders

The Independent Senator from Vermont and self-described “Democratic Socialist” won the hearts of millions of Americans — literally — despite falling short on his bid for president in 2016 and losing the Democratic nomination to Hillary ClintonSanders, 77, was re-elected to a third term as a Senator this year. Sanders boasts extensive political experience, having served in public office since 1981, when he began his term as mayor of Burlington, Vermont. Some have expressed concern over his old age (he would be 79 in 2020) while other supporters seem to remain confident that if he runs on a similar platform to the one he campaigned on in 2016 — focusing on issues like income inequality, jobs, Medicare-for-all, and more — he could gain higher support in his second bid.

3. Elizabeth Warren

The Massachusetts Senator, like Sanders, has cemented her image as a progressive liberal who isn’t afraid to go after big corporations like Wall Street banks for their corrupt practices. She is one of the many Democrats to have been slowly mounting a 2020 presidential campaign in recent weeks. Unless her ideas are deemed too extreme for a majority of Democratic voters — or unless her fight to prove her Native American heritage significantly turned off more people than initially believed — Warren could become a viable contender in 2020. She has also slammed Trump’s policies at every chance she gets.

4. Kirsten Gillibrand

The New York Senator has spoken up repeatedly on several issues like sexual harassment and “Don’t Ask, Don’t Tell,” as well as other military-related issues. Despite being a moderate Democrat for some time, Gillibrand recently showed she is leaning more to the left on certain issues when she revealed she supports a federal job guarantee.

5. Cory Booker

Booker, 49, is one of the youngest candidates whose names has been floated for president in 2020. The Senator from New Jersey has made clear that he will not stand for injustice of any kind, racial or otherwise. There were mixed reactions to his berating of Homeland Security Secretary Kirstjen Nielsen in a public hearing after Trump made his infamous “s—hole countries” comment about African nations, Haiti and El Salvador during a Cabinet meeting in January.

6. Michael Bloomberg

Bloomberg recently re-registered to vote as a Democrat in October, after being a Republican and then an Independent after that. The former New York City mayor is well-liked by many and is a self-made millionaire — unlike Trump, whom he has blasted multiple times. In June, Bloomberg pledged $80 million to Democrats to restore the party’s control over the House of Representatives, and Democrats eventually won the majority in Congress in the midterm elections.

7. Sherrod Brown

The Ohio Senator won his re-election bid for a third term this year after beating Republican Rep. Jim Renacci in November. Brown is the only incumbent Democrat elected to statewide office in Ohio.

8. Eric Holder

Barack Obama‘s former attorney general is known for not being afraid to speak his mind. In October, he drew some criticism from conservatives after he said of the GOP — just weeks before the midterm elections — “when they go low, we kick them,” seemingly putting a twist on Michelle Obama‘s famous “when they go low, we go high” during the 2016 election, funny enough. Holder has not explicitly said he’s running in 2020, but he is set to play a major role in helping Democrats escape another redistricting and gerrymandering fight following the 2020 Census.

9. Kamala Harris

Like Booker, Harris is a young, African-American lawmaker who has demonstrated she is prepared to ask tough questions and demand answers, as shown by her performances in Senate hearings. The Senator from California is perhaps one of the top three Democratic women — along with Warren and Gillibrand — who has been most actively hinting at a 2020 run, especially since the 2018 midterm elections ended. However, also like Booker, some voters may think Harris would be more suited as a vice presidential candidate than a contender at the top of the ticket.

10. Beto O’Rourke

The 46-year-old charismatic U.S. Representative from Texas fell short in his Senate bid this year against incumbent GOP Sen. Ted Cruzbut came much closer than expected. O’Rourke, who is also a former El Paso City Council member, has bashed Trump, Cruz and the Republican establishment many times, and has also criticized PAC and corporate money’s heavy influence in American political campaigns. The progressive O’Rourke even drew comparisons to the inspiring Obama when he first ran for president in 2008. Nevertheless, it remains to be seen if O’Rourke might end up as a presidential candidate or as a running mate for a more experienced Democratic nominee in 2020.

Here are more potential 2020 Democratic nominees whose names have been floated in recent months:

11. Mitch Landrieu

12. Deval Patrick

13. Terry McAuliffe

14. Chris Murphy

15. Andrew Cuomo

16. Julian Castro

17. Eric Garcetti

18. John Hickenlooper

19. John Kerry

20. Amy Klobuchar

21. Jeff Merkely

22. Tim Ryan

23. Adam Schiff

24. Tom Steyer

25. Eric Swalwell 

26. Tulsi Gabbard

27. Peter Buttigieg 

28. Rep. John Delaney

29. Richard Ojeda

30. Andrew Yang