A new national poll points to an extremely close contest between President Trump and Democratic challenger Joe Biden as the race for the White House shifts to a likely general election battle between the two.

Biden, the former vice president and all-but-certain 2020 Democratic presidential nominee, stands at 48 percent support among registered voters nationwide in a Monmouth University poll, with the GOP incumbent at 45 percent. Biden’s slight 3-point edge over Trump is within the poll’s sampling error, meaning the race is roughly tied between the two candidates.

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Three percent said they would vote for an independent candidate in November’s general election, and 4 percent said they were undecided in the survey, which was conducted March 18-22 and released on Tuesday.

According to the poll, the president enjoys a nearly 2-to-1 margin over Biden in the 2,500 solidly red counties that Trump overwhelming won four years ago over 2016 Democratic nominee Hillary Clinton. In the 360 solidly blue counties where Clinton crushed Trump, Biden is up by a 2-to-1 margin. But in the approximately 300 swing counties where the margins in the 2016 presidential election were 10 points or less, Biden tops Trump 50-41 percent.

“The race looks tight right now between Trump and the probable Democratic nominee. But as we learned in 2016, the outcome will be determined by the Electoral College rather than the national popular vote. The poll results suggest Biden may actually be starting out with an advantage in crucial swing areas of the country,” Monmouth University Polling Institute Director Patrick Murray said in a statement.

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As expected, there’s a wide partisan divide, with Democrats backing Biden 89-6 percent and Republicans behind the president 90-7 percent. Independents are nearly dead even, with 45 percent for Trump and 44 percent for the former vice president.

Biden leads 56-34 percent among voters under age 35, Trump has a 53-40 lead among those 35 to 54 and Biden has a slight 4-point advantage among voters 55 and older.

It’s been a week since Biden swept major primaries in Florida, Illinois, and Arizona – cementing his position as the likely Democratic presidential nominee and all but closing Sen. Bernie Sanders’ narrow pathway to the White House. The same day, Trump officially clinched the GOP presidential nomination.

The Monmouth University poll was conducted using live telephone operators, with 754 registered voters nationwide questioned. The survey’s sampling error is plus or minus 3.6 percentage points.