This will be a crucial week for President Donald Trump, with several tests of his credibility looming on Capitol Hill.

Trump's position seems to be weakening. The latest Gallup poll, released Sunday, finds that only 37 percent of Americans approve of his job performance, down from 45 percent a week earlier and his lowest rating yet. Fifty-eight percent disapprove of the way he is doing his job. It's the lowest approval rating for any president at the two-month mark of his first term since 1945, according to Gallup.

Trump's rating could sag further if he suffers setbacks on Capitol Hill and seems unable to get things done or finds his credibility taking more hits.

The first tests come Monday. The House Intelligence Committee is scheduled to hold a public hearing on Trump's accusation, made without citing evidence, that former President Barack Obama illegally ordered wiretapping of Trump Tower, Trump's residence and 2016 campaign headquarters in New York. FBI Director James Comey is expected to testify. It isn't known what Comey will say but committee leaders have announced they have no evidence that Trump's charges were true.

On Sunday, Rep. Devin Nunes, R-Calif., the committee chairman, told Fox News, "Was there a physical wiretap of Trump Tower? No, there never was, and the information we received Friday [from the Justice Department] continues to lead us in that direction."

Rep. Adam Schiff, D-Calif., the committee's top Democrat, told NBC, "We are at the bottom of this. There is nothing at the bottom."

In a series of tweets on March 4, Trump wrote that he "just found out that Obama had my 'wires tapped' in Trump Tower just before the victory." He said Obama's actions were similar to "McCarthyism" – a reference to Wisconsin Sen. Joe McCarthy's ruthless hunt for communists In government during the 1950s. Trump also wrote on Twitter, "How low has President Obama gone to tapp [sic] my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!"

Democrats are ready to attack. "It was such a deceitful claim by the president that I hope Director Comey clears it up once and or all – that what we all suspect is true, and what the evidence so far has shown, which is that it did not occur, that President Obama did not order the wiretapping of candidate Trump," Rep. Eric Swalwell, the leading Democrat on a key Intelligence oversight subcommittee, told Politico.

At Monday's hearing, the Intelligence Committee will also examine whether Russia improperly interfered in the 2016 presidential election and whether there is or has been a criminal investigation of Trump or his campaign aides over ties to Moscow. Congressional investigators are looking into possible collusion between the Trump campaign and Russia to harm the campaign of Democratic presidential nominee Hillary Clinton.

In addition, Trump's nominee for the Supreme Court, Neil Gorsuch, is scheduled for several days of hearings in the Senate Judiciary Committee starting Monday. Gorsuch is expected to face harsh questions from Democrats about his views on many topics including a women's right to choose an abortion, worker safety, the powers of the executive branch and protection of an individual's right to practice religion. But Gorsuch has shown himself to be an affable and intelligent nominee, and unless there is a devastating revelation he is expected to eventually win confirmation in the Republican-dominated Senate. This would give Trump a much-needed victory.