New battleground state polls sent tremors through Democratic circles Monday, underlining that President Trump has a fighting chance of reelection despite his mediocre national standing.

The polls, from The New York Times and Siena College, tested the three leading Democratic 2020 candidates - former Vice President Joe Biden and Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.) - against Trump in the six states that Trump carried by the narrowest margins in 2016.

Those states are Arizona, Florida, Michigan, North Carolina, Pennsylvania and Wisconsin

The polls showed Warren defeating Trump only in Arizona, Sanders doing so in three of the states and Biden doing so in four. All of the Democrats lost to Trump in North Carolina, which President Obama carried narrowly in 2008.

Even in Biden's case the results were hardly conclusive. His edge was 5 points in Arizona and smaller everywhere else: 3 points in both Pennsylvania and Wisconsin, and just 2 points in Florida.

The differences between the Democratic candidates were also not large enough to come to confident judgments as to their real strengths - often, all three were bunched together within the polling margin of error in each state.

But the more troublesome aspect for many Democrats was Trump's showing.

"Any Democrat who looks at that data should be concerned," said Democratic strategist Hank Sheinkopf. "The blue-collar rift in this country hasn't been healed in any way and Trump still commands tremendous loyalty" among his supporters.

Trump famously lost the popular vote to Democrat Hillary Clinton in the 2016 election by almost 3 million votes.

But his narrow victories in Pennsylvania, Wisconsin and Michigan - three states that had been thought to constitute a Democratic "blue wall," having not backed a Republican for president since the 1980s - were enough to get him to the Oval Office.

A 1-point margin of victory in Florida delivered Trump another 29 electoral votes. As he notes in speeches to this day, Trump was a comfortable victor in the Electoral College, taking 306 votes to Clinton's 232.

The fear for Democrats is that he could pull off a similar feat next year.

Trump struggles badly in national polls. An NBC News-Wall Street Journal poll released over the weekend put him 9 points behind Biden and 8 points behind Warren nationwide.

But Democrats are keenly aware that is not how the election will be decided.

"The difference between winning California by 15 or 20 points doesn't matter," said Morgan Jackson, a North Carolina-based Democratic strategist. "Winning states like Wisconsin or Michigan or North Carolina by 1 or 2 points or losing them by 1 or 2 points is what matters."

Jackson, who is not aligned with any presidential candidate in this cycle, said Biden looked "at this time" to be the strongest nominee against Trump. But he cautioned that other candidates could have strength or enthuse voters in demographic groups with which Biden is not so strong - young voters, for example.

Terry Madonna, a professor of public affairs and a polling expert at Pennsylvania's Franklin & Marshall College, was more adamant that Biden would be the best candidate in the Keystone State and elsewhere in the Rust Belt.

"I am a firm believer that the last person Donald Trump wants to run against is Joe Biden," Madonna said. "There is no doubt that Biden would be tough to beat in Pennsylvania. ... He is a moderate, he is not a cultural liberal."

While the new polling made for unnerving reading for some Democrats, others argued that the general landscape was still very favorable for 2020.

Trump carried the three "Blue Wall" states by extremely small margins that they hope to reverse, especially given that his overall approval ratings continue to be anemic at best.

"The 'horserace' is less important than that the president's approval numbers are in the low 40s," said Jill Alper, a Michigan-based Democratic strategist.

Asked about her outlook for Michigan in 2020, she professed confidence.

"I'm very optimistic, not only because of the results of the 2018 election but because there is an apparatus in place to generate the vote, and voters here seem to know that they are working hard for less," Alper said.

Still, the new polls have affirmed that, for all the controversies he has generated, ousting Trump at the ballot box can't be taken for granted by Democrats.

"There is not going to be a blowout on either side," said Jackson. "It will come down to a lot of these [battleground] states that are going to be decided by 1 or 2 points."

Sheinkopf had a warning of a different kind.

When it comes to the battleground states, he said, "Trump is doing pretty good."

The Memo is a reported column by Niall Stanage, primarily focused on Donald Trump's presidency.