Hillary Clinton. Yana Paskova/Getty Images Hillary Clinton's big lead over Donald Trump evaporated in a major poll released Thursday.

The CBS News/New York Times poll, conducted July 8-12, found that Clinton and Trump were in a dead heat in the presidential race, each garnering 40% support.

Clinton had held a 43%-to-37% advantage in the CBS/Times poll from June.

"Great new poll — thank you America!" Trump tweeted Thursday morning with the results attached.

Clinton's dip in the poll came after FBI Director James Comey said she was "extremely careless" with classified information while she was secretary of state (though he declined to recommend charges against her).

Sixty-seven percent of respondents said Clinton wasn't honest and trustworthy, up from 62% in June. Just 28% said she was honest.

Trump's marks, however, weren't much better, with 62% viewing him as dishonest and two-thirds of respondents saying he was not ready to assume the presidency.

When Gary Johnson, the former New Mexico governor who is the Libertarian presidential nominee, was inserted into the poll, Clinton and Trump remain tied at 36%, while Johnson garnered 12% of the overall support.

The margin of error for the July poll was 3 points, and the sample size was 1,600 random adults, with roughly 1,400 being registered voters.