In almost every poll, former Vice President Joe Biden has led the Democratic presidential field. But among the Democrats who work for representatives and senators, he’s behind.

Queried earlier this month by CQ Roll Call, those aides said by a margin of 45 percent to 39 percent that Massachusetts Sen. Elizabeth Warren has the Democrats’ best shot at beating President Donald Trump in the 2020 election.

[Even Joe Biden was once the upstart]

Of the 63 who responded to the Capitol Insiders Survey, most were even more confident that Warren would secure the nomination, with 58 percent of the aides saying so, compared to 34 percent who thought it would be Biden.

More than four months before Democrats caucus in Iowa, launching the primary season, Democratic aides on Capitol Hill see it as a two-person race. No other Democratic candidate came close to Warren and Biden.

CQ Roll Call sent the poll by email to aides on Sept. 10. They had until Sept. 13 to respond. In addition to the Democrats, 60 Republicans and two independents filled out the survey.

Republican aides have coalesced around Trump, with 61 percent saying they wanted him to win the party’s nomination, compared to 13 percent favoring Mark Sanford, the former governor and representative from South Carolina. Former Massachusetts Gov. Bill Weld had the support of 7 percent of the GOP aides who responded.

[Opinion: Joe Biden is old. Who cares?]

That reflects how the GOP establishment, once skeptical of Trump, has fallen in line behind the party’s rank and file. On the eve of the 2016 election, a plurality of GOP respondents to CQ Roll Call’s poll, 38 percent, said they planned to vote for a third-party candidate. Only 30 percent committed to Trump, and 18 percent said they’d back the Democrats’ candidate, Hillary Clinton.

Republican respondents also see the Democrats’ race as a two-person field, but a plurality of them, 42 percent, said they thought Biden would triumph.

As to who was more likely to beat Trump, the GOP aides don’t see it as a difficult question: 67 percent said Biden, while Warren came second at 6 percent.

When it comes to the general election, both sides are feeling confident, with 2 in 3 of the Democratic aides predicting their candidate would beat Trump, and 3 in 4 of the Republicans saying Trump will secure a second term.

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In the race for control of Congress, meanwhile, there’s agreement.

Neither side expects the balance of power to shift.

Republican aides, by a margin of 60 percent to 21 percent, said Democrats would continue to control the House, while 94 percent of those staffers said the GOP would keep the Senate.

Democratic aides were even more confident of their hold on the House, with 98 percent predicting they’d get another term in the majority. But by a margin of 52 percent to 32 percent, they predicted Republicans would retain the Senate.

The rest of the respondents weren’t sure.