For the first time since mid-July, Hillary Clinton has fallen behind Donald Trump in a new national poll.

The latest poll by the right-leaning Rasmussen Reports shows Trump leading 40 percent-39 percent among likely U.S. voters, putting the race within the poll's margin of error. Last week, Clinton led by 4 points, 42-38.

Libertarian candidate Gary Johnson now earns 7 percent (a 2-point drop over two weeks), and Green Party candidate Jill Stein picks up 3 percent. Another 3 percent like some other candidate, and 7 percent are undecided.

Since hitting a high of 44 percent in early August following the Democratic National Convention, Clinton's support has been trending down. She hasn't been at 39 percent support since mid-July.

But Trump is sliding too, as he had 44 percent in mid-July.

The problem for Clinton and Trump appears to stem from support in their respective parties. Clinton has 73 percent of the Democratic vote, down from 79 percent in last week's survey. Trump has dropped 5 points over that time among Republicans, from 76 percent to 71 percent.

The poll of of 1,000 likely voters was conducted Aug. 29-30 and carries a margin of error of plus or minus 3 percentage points.