Donald Trump. Joe Raedle/Getty Images Donald Trump is gaining ground on Hillary Clinton in three of the Rust Belt's most important states, according to polls released on Monday.

Emerson College released surveys that showed Trump even with Clinton in Ohio, trailing the Democratic nominee by 3% in Pennsylvania, and behind her by 5% in Michigan.

Trump has targeted all three states as being crucial to victory, and losing all three would make it virtually impossible for him to win the presidency.

No candidate has won the presidency without carrying Ohio since President John F. Kennedy in 1960.

The polls pull Trump closer to Clinton in the RealClearPolitics polling average in the three states, where he trails the former secretary of state by 3.2% in Ohio and 8.6% in both Pennsylvania and Michigan.

The polls included Libertarian nominee Gary Johnson and Green Party nominee Jill Stein.

Emerson's samples consisted of 800 likely general-election voters in each poll, with a margin of error of 3.4 percentage points. Emerson used landlines exclusively in the poll.