Washington (AFP) - A nationwide Fox News poll released Sunday shows President Donald Trump trailing former vice president Joe Biden and no fewer than four other Democratic contenders as early campaigning for the 2020 election begins to gain steam.

A separate survey of key battleground states, by CBS, shows Democrats strongly favor Biden as the candidate most likely to beat Trump in next year's elections.

While the latest polling news proved heartening to Democrats, the Trump re-election campaign reportedly has cut ties to three of its own pollsters after some of their results -- showing Trump trailing far behind Biden in key states -- leaked.

The Fox poll showed Biden leading Trump by 49 percent to 39 percent among all registered voters nationwide, while Senator Bernie Sanders held nearly the same advantage over the president, at 49 percent to 40 percent.

Holding edges of 1 or 2 points over Trump -- albeit within the poll's three-point margin of error -- were senators Elizabeth Warren and Kamala Harris, as well as Mayor Pete Buttigieg of South Bend, Indiana.

The polling comes more than 500 days before the November 3, 2020 election, an eternity in the political world. One widely viewed tweet this week shows five presidential candidates in recent decades who trailed at this point in their campaigns -- including Trump -- but who went on to win.

The president does not officially launch his re-election campaign until Tuesday, when he plans an elaborate, rally-style event in a huge arena in Orlando, Florida.

- Battleground states -

Still, the Fox poll, conducted June 9 to June 12, was welcomed by Democrats eager to chip away at Trump's popularity, particularly in battleground states such as Pennsylvania and Wisconsin.

The president's campaign had recently dismissed leaked data from its own pollsters showing Biden with double-digit leads in some critically important states, including Florida, Pennsylvania and Wisconsin -- three states Trump won in 2016.

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Trump himself denied the data -- "those polls don't exist," he told ABC -- but his campaign later acknowledged the negative news while discounting it as "ancient" because it dated from March.

On Sunday, The New York Times reported that the president's campaign, furious over the data leak, was cutting ties to three of its five pollsters. They included Polling Company, the former firm of close Trump adviser Kellyanne Conway.

And NBC quoted Trump campaign manager Brad Parscale as conferring a positive spin on the latest results, saying "the president's new polling is extraordinary and his numbers have never been better."

- Warren on the rise -

The new CBS poll, conducted May 31 to June 12, confirms a significant Biden lead in battleground states among Democratic voters, as the crowded race for that party's nomination begins to take shape.

Those voters told pollsters that their support was based above all on a sense that Biden was the candidate best positioned to defeat Trump in 2020.

The CBS News/YouGov Battleground Tracker survey found that Biden had the backing of 31 percent of Democratic voters in 18 key states, ahead of senators Elizabeth Warren (17 percent), Sanders (16 percent) and Kamala Harris (10 percent).

The poll, with a 1.5 percent margin of error, was conducted in influential early-voting states including Iowa, New Hampshire and South Carolina, as well as in populous states in the upper Midwest where Trump eked out narrow but decisive victories in 2016.

Elizabeth Warren has been steadily rising in the polls, while Sanders' support has slipped.

He acknowledged on Sunday that "polls go up and polls go down," but insisted that the survey showed he was well-placed to defeat Trump.

"I think we can win in Pennsylvania, Wisconsin and Michigan and some of the other battleground states," the self-styled democratic socialist told "Fox News Sunday."

Democrats begin more earnestly winnowing down their large field of candidates when they hold successive nights of televised debates on June 26 and 27.

The Fox poll found that Democratic voters, by roughly three-to-one, favor a nominee who would provide "steady, reliable leadership" rather than a "bold new agenda."

But Representative Alexandria Ocasio-Cortez, the fiery 29-year-old New Yorker who has emerged as a heroine to young voters and progressives, suggested Sunday that Democrats could be in trouble if they fail to nominate an energizing candidate with working-class appeal.

She said she would support the 76-year-old Biden if he wins the nomination but added on ABC that "we have to really factor in the enthusiasm of voters."

"We need to pick a candidate that's going to be exciting to vote for -- all people, women, people of all genders, races, income levels."