In Florida, Clinton and Trump each garner 47 percent. In Ohio, Trump earns 46 percent, and Clinton has fallen, by 4 percentage points in the last month, to 45 percent.
Meanwhile, in North Carolina, where Mitt Romney won in 2012, Clinton gets 47 percent to 43 percent for Trump. And in Pennsylvania, Clinton polls slightly lower than previously but still ahead of Trump, at 48 percent support to Trump's 43 percent.
All four states are within the polls' margin of error, and winning all of them would be Trump's best chance to make it to the White House. With the electoral votes from these four states, Trump would likely win a majority in the Electoral College.
However, a win for Clinton in Ohio, Florida or North Carolina would likely seal a victory for her campaign.
Clinton's slight decline in Ohio and larger decline in Pennsylvania show classic signs of a fading post-convention bounce. Democratic voters in both states seem to be softening a bit from last month. And Clinton's advantage among women, especially white women, is shrinking in Pennsylvania while Trump's lead among men in Ohio is climbing.
North Carolina presents a unique challenge for Trump. Although he leads by more than 20 percentage points among military households in Florida, Ohio and Pennsylvania, he runs neck and neck with Clinton among the large military population in North Carolina.
The poll shows almost no gender gap among Republicans and Democrats, but a wide split by gender among independents.