WASHINGTON -- U.S. Sen. Cory Booker remained in fifth place on the Washington Post's most recent list of the most likely 2020 Democratic presidential candidates.

Booker, D-N.J., trailed only U.S. Sens. Bernie Sanders, I-Vt.; Elizabeth Warren, D-Mass., and Kamala Harris, D-Calif., and former Vice President Joe Biden on the newspaper's quarterly list. They were the same potential candidates ahead of him in March.

He has been out front on some major issues, such as legalizing marijuana at the federal level; outshined some of his possible rivals at a recent gathering of the Democratic National Committee; and has been a prominent speaker at progressive gatherings.

In addition, Booker has traveled the country in support of fellow Democrats, such as U.S. Sen. Doug Jones, D-Ala. He is expected to help out more in the midterm elections, which are seen as a referendum on President Donald Trump.

He has used his post on the Senate Judiciary Committee to oppose Trump. Last month, he asked the panel to delay consideration of a Supreme Court nominee because it would be a "potential conflict of interest" for Trump while members of his administration and presidential campaign remain under federal investigation over possible ties to Russia.

And he garnered national attention for his January takedown of Homeland Security Secretary Kirstjen Nielsen, refusing to believe that she did not hear Trump refer to Haiti and some African nations as "shithole countries" during an Oval Office meeting with members of Congress.

Booker has said he won't make a decision on a presidential run until after the midterms this November. He also has to decide whether to run for re-election; his Senate term expires in January 2021.

The Post's latest top 10:

1. Sanders

2. Warren

3. Harris

4. Biden

5. Booker

6. U.S. Sen. Kirsten Gillibrand, D-N.Y.

7. Former Massachusetts Gov. Deval Patrick

8. Former Virginia Gov. Terry McAuliffe

9. Former U.S. Attorney General Eric Holder Jr.

10. Former New York City Mayor Michael Bloomberg

Jonathan D. Salant may be reached at jsalant@njadvancemedia.com. Follow him on Twitter @JDSalant or on Facebook. Find NJ.com Politics on Facebook.