A poll conducted March 5 through March 7 shows that President Donald Trump still leads former Vice President Joe Biden in a matchup in key battleground states.

The Firehouse Strategies and Optimus poll reveals, however, that the margin between the two candidates is slim.

In Michigan and Wisconsin, Trump leads Biden by two points. In Pennsylvania, Trump leads Biden by one point.

Biden has strengthened his support as the former vice president trailed Trump by nine points in Wisconsin when the same poll took the temperature of voters in December. Sen. Bernie Sanders does worse against Trump in the three swing states — seven points behind Trump in Michigan, four points behind Trump in Pennsylvania, and six points behind Trump in Wisconsin.

The former vice president has benefited from clearing the 2020 Democrat presidential field but does not lead the president.

In Michigan, Trump leads with 46 percent against Biden at 44 percent. In Pennsylvania, Trump leads with 45 percent, while Biden garners 44 percent. In Wisconsin, Trump leads with 45 percent while Biden gets 43 percent support.

Trump leads Sanders 48 percent to 41 percent in Michigan, 46 percent to 42 percent in Pennsylvania, and 48 percent to 42 percent in Wisconsin.

The survey was conducted March 5 to March 7 with 1,582 likely voters in Wisconsin (N = 502), Michigan (N = 550), and Pennsylvania (N = 533). The margins of error are approximately ± 4.7% in Wisconsin, ± 4.6% in Michigan, and ± 5.0% in Pennsylvania.