A majority of Americans report grave suspicions about President Trump’s firing of FBI Director James B. Comey and his conduct during investigations of Russia’s interference in the 2016 election, according to a new Washington Post-ABC News poll.

A 56 percent majority of U.S. adults say Trump is interfering with such investigations rather than cooperating, while 61 percent say Trump fired Comey to protect himself rather than for the good of the country.

[Top intelligence official told associates Trump asked him if he could intervene with Comey on FBI Russia probe]

Comey also faces serious credibility problems ahead of his highly anticipated Senate testimony Thursday, with 36 percent of Americans saying they trust what he says about Russia and the election “a great deal” or “a good amount,” while 55 percent trust him less or not at all. The poll finds substantial skepticism across party lines, evidence that his role investigating the campaigns of Hillary Clinton and Donald Trump has taken a toll.

[Read full poll results | How the poll was conducted]

Trump is seen as even less trustworthy, however, with just over 1 in 5 saying they trust what he says about Russia’s role in the 2016 campaign, while just over 7 in 10 trust him less. Fully half of adults say they do not trust what Trump says “at all” on these issues, compared with one-quarter who say the same of Comey. Fully 4 in 10 Americans have doubts about both Comey and Trump’s statements on Russia and the election.

The Post-ABC poll was conducted Friday to Sunday, before The Washington Post reported Tuesday that the Director of National Intelligence told associates that Trump asked him if he could intervene with Comey on the FBI's Russia probe to back off its focus on former national security adviser Michael Flynn.

In May, Trump was widely criticized for firing Comey, who was leading a counterintelligence investigation to determine whether associates of Trump may have coordinated with Russia to interfere with last year's presidential election. Trump's shifting explanations for removing Comey provoked questions about his motivations, as did an interview with NBC News where Trump said he made his decision with “the Russian thing” on his mind.

Democrats are nearly united in their suspicions of Trump, with 88 percent saying he fired Comey in May to protect himself and 87 percent saying Trump is trying to interfere with investigations of possible Russian influence in the election.

Political independents, a group that Trump won in last year’s election, are also largely critical. By 63 to 20 percent, more independents say Trump fired Comey to protect himself rather than for the good of the country. And by roughly 2 to 1, more independents say Trump is trying to interfere with Russia investigations rather than cooperating with them (58 to 27 percent). More than three-quarters of independents say they trust Trump’s statements about Russia “just some” or not at all.

Large majorities of Republicans say Trump fired Comey for the good of the country (71 percent) and that he is cooperating with investigations into Russia’s election influence (77 percent). At the same time, roughly 1 in 5 Republicans say Trump fired Comey to protect himself, while about 1 in 6 think he is trying to interfere with investigations, criticisms shared by more than 3 in 10 conservatives.

Trump’s trustworthiness also lags among fellow partisans, with less than half of Republicans (45 percent) saying they trust what he says about Russia investigations “a great deal” or “a good amount,” while about as many trust him less (48 percent).

Comey’s credibility on Russia investigations also has a partisan tinge, with 54 percent of Democrats saying they trust what he says compared with 32 percent of independents and 18 percent of Republicans. Even among Democrats, whose leaders have decried Comey’s firing, about 4 in 10 say they trust the former FBI director “just some” or “not at all.” Those doubts rise to 59 percent among independents and 76 percent among Republicans, ample skepticism ahead of the former FBI director’s testimony this week.

The Post-ABC poll was conducted Friday to Sunday among a random national sample of 527 adults, including users of cellular and landline phones. The margin of sampling error for overall results is plus or minus five percentage points.