Former Vice President Joe Biden is holding a national lead over his rivals for the Democratic presidential nomination, but Sen. Elizabeth Warren of Massachusetts is gaining on him, the latest ABC News/Washington Post poll shows.

The Democratic candidates are scheduled to debate again Thursday night in Houston, and this could shuffle the deck. But for now, Biden remains the national front runner with support from 27% of Democrats and Democrat-leaning independents. Sen. Bernie Sanders of Vermont has 19% and Warren has 17%. This represents a decline of 2 points for Biden from 29 percent in early July, a drop of 4 points for Sanders from 23 percent in early July, and a gain of 6 points for Warren from 11 percent during the same period.

The rest of the Democratic candidates are far behind, according to the poll released Sunday.

Biden holds a continued advantage on perceived electability. Forty-two percent of Democrats and Democrat leaners see him as the candidate with the best chance to defeat Republican President Donald Trump, down slightly from 45% in July. Sanders has 14% on electability and Warren, 12%.