Hillary Clinton's polling lead over Donald Trump in several swing states is shrinking in part because of non-white and women voters, according to a new national poll. Florida, North Carolina, Ohio and Pennsylvania are up for grabs as the Democratic and Republican presidential nominees battle for supremacy in states that could prove to be the difference come Election Day.

Trump is leading Clinton in Ohio even when Libertarian Party nominee Gary Johnson and Green Party nominee Jill Stein are taken into account, but the former secretary of state was enjoying a slim lead in the rest of the swing states in both head-to-head matchups with the New York billionaire as well with the third party candidates factored in, according to the latest Quinnipiac University Poll published Thursday. Clinton's lead in Pennsylvania has also been trimmed by Trump, reducing the gap to at least six percentage points — five percentage points in a head-to-head matchup.

"The obvious takeaway from these numbers is that Donald Trump has staged a comeback from his post-Democratic convention lows, especially in Pennsylvania and Ohio," said Peter A. Brown, assistant director of the Quinnipiac University Poll. "Taking a bit longer view, however, we see a race that appears little changed from where it was as the GOP convention began in July, and at least in these four key states is very much up for grabs."

Many white voters continue to support Trump, but it is Clinton's support among non-whites that could be proving to be the difference, as she is enjoying an overwhelming lead in that demographic in all four swing states. However, the lack of support for Trump from women cannot be ignored, as Clinton is also leading among women voters in the four states, as well. 

Republicans have already admitted that three battleground states — Colorado, New Hampshire and Virginia — are unwinnable for Trump, Politico reported.

The difference could be in Clinton's aggressive approach to advertisements, for which she has lopsidedly outspent Trump, NPR reported. She has nearly $30 million to spend in Ohio compared to about $5 million from Trump. Likewise in Florida and North Carolina, Clinton is enjoying a substantial advantage when it comes to ads there.

While the presidential race has indeed gotten much closer, with Trump even leading Clinton in at least one national poll, the former secretary of state still has a very good chance to win the White House, one polling expert said, Voice of America reported.

"There's no guarantee she (Clinton) will win, but the odds currently favor her," said Larry Sabato, Director of the Center for Politics at the University of Virginia in Charlottesville.

Real Clear Politics confirms that prediction, with Clinton holding a very slim lead nationally in a roundup of nine polls taken recently. Of those polls, Trump is leading in one and tied in another.

In Florida, the Quinnipiac poll surveyed 761 voters with a margin of error of 3.6 percentage points; 751 North Carolina voters with a margin of error of 3.6 percentage points; 775 Ohio voters with a margin of error of 3.5 percentage points; and 778 Pennsylvania voters, also with a margin of error of 3.6 percentage points.