WASHINGTON — Former Vice President Joe Biden and Sen. Elizabeth Warren, D-Mass., lead the Democratic presidential field, according to the national NBC News/Wall Street Journal poll’s opening measure of the 2020 horse race.

Biden gets the support of 26 percent of voters who say they will participate in next year’s Democratic primaries or caucuses, while 19 percent back Warren.

They’re followed by Sens. Kamala Harris, D-Calif., and Bernie Sanders, I-Vt., who are tied at 13 percent.

South Bend, Indiana, Mayor Pete Buttigieg gets support from 7 percent of Democratic primary voters, and former Texas Congressman Beto O’Rourke and entrepreneur Andrew Yang are at 2 percent.

No other candidate gets more than 1 percent.

Biden performs best among African Americans, older Democrats and those who are moderate or conservative in their political views, while Warren runs strongest with self-described liberals and those ages 18 to 49.

Sanders also performs best among the youngest Democratic primary voters.

This NBC/WSJ poll was conducted July 7-9, after the first Democratic debates and the subsequent candidate skirmishes over the issues of race and health care.

New candidate Tom Steyer didn’t enter the race until July 9, and the survey didn’t test support for the billionaire activist.

The poll also asked Democratic primary voters about their second choice for president. The top responses were: Harris (14 percent), Warren (13 percent), Sanders (12 percent) and Biden (10 percent).

But importantly, only 12 percent of all Democratic primary voters said their mind is definitely made up, which suggests how malleable these numbers are.

“Every result looks so meaningful, so significant. And in truth, it is only July 2019,” cautioned Democratic pollster Peter Hart, who conducted this survey with Republican pollster Bill McInturff.

“They are looking at lots of candidates,” McInturff said of these voters, “and they don’t need to make a choice right now.”

A tale of two different Democratic primaries

The poll also shows how the Democratic electorate is divided — between voters who want substantial change and those who want smaller change.

Fifty-four percent of Democratic primary voters say they prefer a nominee who proposes larger-scale policies that might cost more and be harder to pass — but could still result in major change.

Among these voters, Warren leads the pack (at 29 percent), followed by Sanders (18 percent), Biden (16 percent) and Harris (14 percent).

By contrast, 41 percent of Democratic primary voters say they want a nominee who pushes for smaller-scale policies that cost less and might be easier to pass — but that bring less change.

And among these voters, Biden holds a substantial lead (at 35 percent), followed by Harris (14 percent), Buttigieg (8 percent) and Sanders (7 percent).

Similarly, Democratic primary voters are divided on what’s more important to them — a candidate who comes closest to their views on issues, or one who has the best chance to defeat President Donald Trump.

Fifty-one percent say issues are more important, and those voters break for Biden (18 percent), Warren (18 percent), Sanders (17 percent) and Harris (11 percent).

That’s compared with 45 percent who believe defeating Trump is more important, and they break Biden (at 34 percent), Warren (21 percent), Harris (16 percent), Buttigieg (8 percent) and Sanders (6 percent).

Democrats back government-run health care — but others don’t

Additionally, the poll finds that more than 7-in-10 Democratic primary voters favor a single-payer health care system in which all Americans get their health insurance from one government plan financed in part by taxes.

But that’s compared with just 36 percent of independent voters and 14 percent of Republicans who back government-run health care.

Among all voters, 44 percent support it, versus 49 percent who oppose it.

Divided on impeachment

Meanwhile, Democratic primary voters remain divided on impeaching Trump: 41 percent believe there’s enough evidence to begin impeachment hearings now, versus 39 percent who say Congress should continue investigating to see if there’s enough evidence to hold impeachment hearings in the future.

Only 19 percent of Democratic primary voters think that Congress should not hold impeachment hearings and that Trump should finish his term as president.

Among all voters, 21 percent support beginning impeachment now; another 27 percent want more hearings; and 50 percent believe the country should move on.

Who impressed the most at the first debates?

Fifty-one percent of Democratic primary voters say they either watched or listened to some of the first two presidential debates, and another 29 percent say they paid close attention to the news coverage of them.

When these respondents were asked which candidates impressed them the most — they were allowed up to three choices — the top answers were Harris, Warren, Buttigieg and Biden.

And interest in the Democratic primary race remains high, with a combined 82 percent of primary voters saying they’re “very closely” or “somewhat closely” following the contest.

“We know they are paying attention,” McInturff, the GOP pollster, said.

The NBC/WSJ poll was conducted July 7-9 of 800 total registered voters — more than half reached by cellphone — and that has an overall margin of error of plus-minus 3.5 percentage points.

Among the 400 Democratic primary voters surveyed, the margin of error is plus-minus 4.9 percentage points.