But it's not all bad news for Trump, who enjoys an 11-point edge over Clinton in Indiana, a state that went narrowly for President Barack Obama in 2008 before swinging to Mitt Romney, who won there by 10 points in 2012.
The Monmouth University poll
of Indiana -- home to Trump's running mate, Mike Pence -- found Trump with 47% support to Clinton's 36% among likely Indiana voters. Libertarian Gary Johnson garnered 10%, while 5% said they were undecided.
A Quinnipiac University swing state poll, meanwhile, found him trailing Clinton by 10 points, 49% to 39%, in a head-to-head matchup in Colorado. With Johnson and the Green Party's Jill Stein thrown into the mix, that margin narrows to 8 points, with Johnson scoring 16% backing.
Virginia breaks down similarly, with Clinton losing only a single point off her 12-point (50% to 38%) head-to-head advantage over Trump when Johnson and Stein are added as options. (Clinton leads with 45%, compared to 34% for Trump, 11% for Johnson and 5% for Stein.)
The race in Iowa is effectively a toss-up, according to Quinnipiac, which gives Clinton a 2-point lead, 41% to 39%, in a four-way race, within the poll's margin of error. Trump is 18 points off Clinton's pace with women voters, and 97% of Democrats in The Hawkeye State are poised to vote for the former secretary of state, while Trump is winning only 85% of Republicans.
Bayh with comfortable lead
Clinton's hopes of entering the White House with a Democratic majority in the Senate also got a boost from the Monmouth poll.
Democratic Senate candidate Evan Bayh has a 7-point advantage (48% to 41%) over Rep. Todd Young in their race to replace retiring
Republican Sen. Dan Coats.
Bayh, who once represented Indiana in the upper chamber and is seeking to return after choosing not to seek re-election in 2010, could supplement his support among Democrats with Trump voters -- 16% of whom said they would split their ballots, according to the Monmouth survey.
Still, he faces many voters who are skeptical of his reasons for returning to politics after years away, with only 31% believing his decision to enter the race comes from "a desire to serve the public."
The Monmouth poll, which reached 403 likely Indiana voters, was conducted from Aug. 13-16. Its margin of error is +/- 4.9%.
Quinnipiac carried out its survey from Aug. 9-17, conducting interviews with 830 likely voters in Colorado, 846 in Iowa and 808 in Virginia. The margin of error in Colorado and Iowa was +/- 3.4% and +/- 3.5% in Virginia.