According to another survey by the pollster, Mr Trump is still managing to hold on to Republican support.
His approval rating is four points higher than the 83 per cent average for previous presidents one month into their presidency, despite his overall approval among Republicans falling three points since his inauguration.
That's near his low-point of 35 percent that Gallup found in late March. Keep up with this story and more Trump had the lowest approval rating of any president at the 100-day mark in the modern polling era and it has shown little sign of improvement.
At this point in their first term, every president dating back to Eisenhower had a better approval rating.
The comments are the latest addition to a growing list of White House rationale for Mr Comey's firing.
Initial statements from the White House said Mr Trump had fired Mr Comey on the recommendation of the Justice Department, due to his handling of the FBI investigation into Hillary Clinton's private email server.
These results cannot be regarded as definitive, since there is variation among pollsters.
Rasmussen's Daily Tracking poll – which often finds Republicans have a high favourability score – recently claimed Mr Trump had an approval rating of 55 per cent, while the Pew Research Centre has said the property mogul had an approval rating of 38 percent.
The Baltimore Sun said of President Bill Clinton in 1993, almost 90 days into his presidency, that "public opinion surveys show him to be the least popular president since the advent of modern polling.” Before Trump, Clinton, in fact, had the lowest 100-day approval rating of any modern president, according to Gallup."The average first-quarter approval rating among those who identify with the president's party had been 83 percent before Trump," writes Gallup’s Jeffrey M. His backing among independents, for instance, has dropped about 15 percent.As the charts below show, the president's approval rating was flat or declined in every poll taken over the last several months.As President Trump approaches his 100th day in office, he's earned one distinction over his predecessors that he probably won't not tout: A historically low approval rating.According to recent polls, Trump will reach 100 days in office with the lowest early approval ratings of any President in modern history.
Later, the president claimed he had fired Mr Comey after deciding that the FBI investigation into his campaign's possible ties to Russia was baseless.