Quinnipiac focused on these three states because no candidate since 1960 has won a presidential race without winning at least two of the three states.
As for Clinton, she would receive 43 percent support in Florida, 40 percent support in Ohio and her support has dropped from 45 percent to 36 percent in Pennsylvania.
While Trump and Clinton are leading in the 2016 presidential election in the three key swing states, they also receive the worst favorability and trustworthiness ratings.
If Vice President Joe Biden were to join the Democratic field -- a decision he's expected to make within days -- he would be the best general election candidate for Democrats, the poll found.
Similarly, the survey indicated Carson would be the best GOP candidate for the general election.
When Biden is factored into the Democratic race, he trails Clinton in both Ohio and Pennsylvania, and Bernie Sanders comes in third. Biden and Sanders would be tied at 19 percent in Florida.
Quinnipiac's last survey of the swing states in August found Biden would outperform Clinton in certain matchups against Trump.
From September 25 to October 5, Quinnipiac surveyed more than 1,000 voters in each of the three swing state with margins of error of about +/- 3 percent.