A Politico/Morning Consult poll released on Tuesday for the third quarter shows plunging approval ratings for most incumbent senators from both parties among all voters.

Republican establishment senators aligned with Senate Majority Leader Mitch McConnell (R-KY) see even more dramatic declines in their net approval ratings among likely Republican primary voters, as reported in “DATA DU JOUR – per Morning Consult,” by Politico Playbook:

The average senator’s approval ranking has dropped by eight net percentage points since the first quarter of 2017. … Among the 25 senators with the largest approval drops over this time period, 18 are Republicans and 7 are Democrats. … Susan Collins’ net approval among Maine Republicans dropped from +38% to -2% over the last quarter, a 40 point swing. Lisa Murkowski’s net approval among Alaska Republicans dropped from +33% to +2%, a 31 point swing. Dean Heller’s net approval among Nevada Republicans dropped from +41% to +16%, a 25 point swing. McConnell is the least popular senator and growing increasingly unpopular: The Senate Majority Leader maintains his title as the least popular senator in America, with 33% of Kentucky voters approving and 55% disapproving. This represents a net 15% drop since Q2.

Among all voters, Republican establishment senators fared poorly as well.

“The most dramatic swings in approval came for Republican Sens. Shelley Moore Capito (W.Va.) and Sen. Cory Gardner (Colo.). Their net rankings both went down 18 percentage points,” Politico Playbook noted:

In Kentucky, one-third of voters approve of McConnell’s job performance, while 55 percent of voters said they disapprove — more than any other senator. In Vermont, 71 percent of voters approve of Sanders, while 22 percent disapprove of Sanders, who ran a stronger-than-expected race in 2016 for the Democratic presidential nomination. McConnell’s net approval, the difference in his approval and disapproval percentages, dropped 15 percentage points, the third-largest drop in the Senate, from the second quarter, according to the survey. The slide came as he failed to advance Obamacare repeal — a key pillar of the GOP’s political agenda since the law’s enactment in 2010.

Only 33 percent of Kentucky voters approve of McConnell’s performance on the job, while 55 percent disapprove. That is a drop of eight points in McConnell’s approval rating of 41 percent at the end of the second quarter and a seven point increase in his second quarter disapproval rating of 48 percent.

Only Sen. Bob Menendez (D-NJ), currently on trial for public corruption on bribery, fared worse than McConnell in terms of third quarter approval.

New Jersey voters gave him only a 32 percent approval rating, while 41 percent disapproved of his job performance. Menendez’s seven point approval rating decline in a single quarter from 39 percent at the end of the second quarter should set off alarm bells for Democratic Party officials in the state, who will be faced with a decision about how to respond to the outcome of Menendez’s trial, which is scheduled to go to the jury for deliberation within days.

If found guilty, the question will become when and how Menendez should be asked to resign. If found not guilty, Menendez might still face a tough battle for re-election. His approval ratings have dipped so low, should he become the Democratic nominee for the U.S. Senate seat in 2018, the unthinkable might be a possibility: a strong GOP candidate taking a surprise November 2018 victory over the tainted Democrat.

The poll results should be taken with more than a grain of salt, however, due to its unusual methodology. While most reliable professional polls are conducted over a two-to-three-day period of 500 to 1,500 respondents using phone interviews to get the most accurate “snap shot” of opinion at any moment of time, the Morning Consult Poll is conducted online over a three month period beginning June 1 and ending September 30 of more than 250,000 respondents in 50 states — an average of 5,000 respondents per state– and is online only.

With that caveat in mind, it is probably best to consider the poll results a lengthy rolling average that may show trends over time when comparing second quarter results with third quarter results of approval and disapproval ratings of senators among all voters.

Among the incumbent senators who are up for re-election in 2018 whose approval ratings are under 50 percent, always a danger sign for incumbents, are:

Sen. Jeff Flake (R-AZ) with a 33 percent approval, 48 percent disapproval rating. (Approval down 4 points, explaining perhaps why he has said he will not run for re-election.)

Sen. Thom Tillis (R-NC), with a 38 percent approval, 41 percent disapproval rating. (Approval down 3 points.)

Sen. Dean Heller (R-NV), with a 39 percent approval, 30 percent disapproval rating. (Approval down 2 points.)

Sen. Claire McCaskill (D-MO), with a 42 percent approval, 39 percent disapproval rating. (Approval down 4 points.)

Sen. Tammy Baldwin (D-WI), with a 41 percent approval, 38 percent disapproval rating. (Approval down 1 point.)

Sen. Bob Casey (D-PA), with a 43 percent approval, 32 percent disapproval rating. (Approval down 3 points.)

Sen. Deb Fischer (R-NE), with a 45 percent approval, 35 percent disapproval rating. (Approval down 4 points.)

Sen. Debbie Stabenow (D-MI), with a 45 percent approval, 36 percent disapproval rating.

Sen. Orrin Hatch (R-UT), with a 46 percent approval, 41 percent disapproval rating. (Approval down 6 points.)

Sen. Sherrod Brown (D-OH), with a 47 percent approval, 28 percent disapproval rating. (Approval down 3 points.)

Sen. Joe Donnelly (D-IN), with a 47 percent approval, 26 percent disapproval rating. (Approval down 6 points.)

Two other Democratic senators up for re-election in 2018 are slightly over 50 percent but have each seen their net approval ratings drop 9 points in the past quarter:

Sen. Joe Manchin (D-WV), with a 53 percent approval, 36 percent disapproval rating. (Approval down 4 points.)

Sen. Heidi Heitkamp (D-ND), with a 55 percent approval, 32 percent disapproval rating. (Approval down 5 points.)

“Not so long ago Republican U.S. Senate candidate Tom Campbell’s campaign released polling showing the challenger ahead of incumbent Senator Heidi Heitkamp,” Rob Port wrote at North Dakota’s popular Say Anything Blog on Tuesday:

There was much scoffing about the poll, as perhaps there should be for any survey conducted and released by a political campaign, but now new numbers from Morning Consult indicate there may be something to the Campbell numbers. Earlier this summer Morning Consult measured Heitkamp’s popularity among North Dakotans at 60 percent, with just 28 percent disapproval. That was good enough to make Heitkamp the 11th most popular member of the U.S. Senate. But now that same poll shows Heitkamp’s popularity has fallen. Her approval rating is down to 55 percent, and her disapproval is up to 32 percent. Her approval rating is down to 55 percent, and her disapproval is up to 32 percent. Heitkamp is still above water, but the news isn’t good for the incumbent who is widely seen as vulnerable heading into the 2018 election.

The only bright spot for the Democrats among senators up for re-election in 2018 is Sen. Jon Tester (D-MT), who has seen has approval ratings climb to 53 percent, while his disapproval rating has dropped to 33 percent.

Other notable ratings of senators not up for re-election in 2018:

Sen. Lisa Murkowski (R-AL), with a 49 percent approval, 38 percent disapproval rating. (Approval down 6 points.)

Sen. John McCain (R-AZ), with a 46 percent approval, 44 percent disapproval rating.

Sen. Cory Gardner (R-CO), with a 40 percent approval, 29 percent disapproval rating. (Approval down 8 points.)

Sen. Susan Collins (R-ME), with a 62 percent approval, 30 percent disapproval rating.