Maine Sen. Susan Collins (R) trails her Democratic challenger — state Rep. Sara Gideon — by 8 points in the latest poll from the Bangor Daily News.

Collins is one of a handful of GOP senators whose race has been labeled a "toss up" by the nonpartisan Cook Political Report.

In the poll, when asked who was their first choice in November's Senate election, 43 percent of respondents said Gideon, while 35 percent said Collins. Gideon's lead was greater among the registered voters surveyed. 

Collins, who has served as one of Maine's senators since 1997, has seen her positivity ratings plummet, most notably among Democrats and independents.

Sixty percent of independents polled said their opinion of Collins had negatively shifted in the past four years, and 80 percent of Democrats said the same. She even struggled within her own party, as 34 percent of Republicans polled said they view Collins more negatively than they did four years ago; 31 percent said they view Collins more positively now than they did four years ago, the start of President Trump's presidency.

Nearly three-fourths of Republican voters said they still back Collins. Gideon's support among Democrats was considerably less at 59 percent, showing that the election will likely come down to swing voters and independents.

The senator also trailed Gideon in a series of other questions. For example, 42 percent of surveyed Mainers said Gideon was principled, and 39 percent said the same for Collins. Additionally, 32 percent said Collins was unprincipled, while only 21 percent said that Gideon lacks scruples.

The poll was conducted July 28-Aug. 9, surveying 500 likely Maine voters.