The poll, conducted April 16-21 among 4,306 American adults, shows that about 42% of respondents approve of Trump's performance as president, down from 43% in a previous poll conducted three weeks earlier and from 47% in the first hours after his Jan. 20 inauguration.
The main sources of disapproval were Trump's moves to punish universities he deemed too liberal and his appointment as chairman of the board of the Kennedy Center.
However, Trump's approval rating remains higher than that of his Democratic predecessor, Joe Biden, for most of his presidency.
The poll also found that 83% of respondents believe the U.S. president should follow the decisions of federal courts, even if he disagrees with them.
Some 57%, including one-third of Republicans, disagreed with the statement that "it's OK for a U.S. president to withhold funding from universities if the president doesn't agree with how the university is being run." At the same time, 66% of respondents said that the president should not control major cultural institutions such as national museums and theaters.
On immigration, Trump’s strongest area of support, 45% of respondents approved of his performance, while 46% disapproved.
Finally, three-quarters of respondents, including 53% of Republicans, do not want Trump to run for a third term.
The poll has a margin of error of about 2%.