President Trump is in the Oval Office in large part because of his narrow victories in Wisconsin, Michigan and Pennsylvania, three states traditionally considered a "blue wall" which crumbled for Democrats in 2016. However, a new poll indicates that Mr. Trump may have trouble holding onto two of those states in 2020.

A Quinnipiac poll released Thursday found all top Democratic candidates leading Mr. Trump in Pennsylvania and Michigan. He trails Joe Biden, Amy Klobuchar and Michael Bloomberg by 6 to 8 percentage points in Pennsylvania, and Bernie Sanders tops Mr. Trump by 5 percentage points in Michigan.

It's not all bad news for the Trump campaign, however, since the president leads all Democrats in Wisconsin by 7 to 11 percentage points.

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Mr. Trump is also viewed more favorably in Wisconsin than in the other two states: 50% of voters say they have a favorable opinion of him. Meanwhile, 54% of voters in Michigan and 52% of voters in Pennsylvania say they have an unfavorable view of the president. The Democratic candidates fare little better, since they are also mostly negatively viewed in all three states.

Thirty-one percent of Wisconsin voters, 29% of Pennsylvania voters and 35% of Michigan voters say the economy is the biggest issue for them in the upcoming election.

"Three different states, three different scenarios, one constant — the economy. It's a top issue for voters, and it's giving President Trump a strong tailwind. Wisconsin voters give him a job approval rating above 50 percent, higher than what he receives nationally and in Pennsylvania and Michigan. These Wisconsin numbers are a red warning sign for Democrats that rebuilding the 'blue wall' in 2020 may not be so easy. But it's a long way to November," said Quinnipiac University Polling Analyst Mary Snow in a statement.

Biden, Klobuchar and Pete Buttigieg have each made the argument that they can win these critically important "blue wall" states, and are therefore best positioned to defeat Mr. Trump in November.

Michigan holds its Democratic primary on March 10, Wisconsin on April 7 and Pennsylvania on April 28.

From February 12 to 18, Quinnipiac University surveyed 845 self-identified registered voters in Michigan with a margin of error of +/- 3.4 percentage points; 849 self-identified registered voters in Pennsylvania with a margin of error of +/- 3.4 percentage points; and 823 self-identified registered voters in Wisconsin with a margin of error of +/- 3.4 percentage points.