Among all adults in the survey, 39 percent approved of Trump's performance, down four points from last month. Fifty-seven percent disapproved of how the president is doing. Forty-four percent strongly disapproved, while 22 percent strongly approved.
There are warning signs for the president in the internal numbers as well, as his core constituencies back away from him a bit.
Trump's approval rating is 79 percent among Republicans, but that represents a five-point decline from last month. Forty-six percent of white voters view Trump's job favorably, down four points since March.
The president had the approval of 50 percent of men last month, but that slipped to 45 percent in April. Thirty-four percent of women approve of Trump's performance.
In one somewhat bright spot for Trump, 36 percent of voters aged 18 to 34 said they approved of his performance – a five-point boost from April. Yet his approval rating among independents is now 38 percent, which is seven points lower than last month's results.
"2018 is shaping up as a referendum on President Donald Trump," Democratic pollster Peter Hart of Hart Research Associates, who conducted the poll with Republican pollster Bill McInturff of Public Opinion Strategies, told NBC News.
Democrats have a seven-point lead over Republicans on the generic congressional ballot for this fall's midterm elections, the poll said, while Democrats have much more intense enthusiasm heading into the pivotal contests.
The poll showed voters favor Democrats by a 47-40 edge on the generic ballot, which is down from a 50-40 lead Democrats had in March. Democrats need to flip 23 seats this fall to secure a majority.
However, 66 percent of Democratic voters have a high level of interest in voting this fall, while 49 percent of Republicans do. A high level of interest is marked by a score of 9 or 10 on 10-point scale.
The percentages are reminiscent of the last time a president was facing intense opposition during his first term. Data from NBC/WSJ polling in 2010, when Republicans seized the majority in the House during President Barack Obama's first term, showed that 66 percent of GOP voters had a high level of interest, while 49 percent of Democrats said as much.
But it's not a "knockout" for Democrats, yet, according to the pollsters. Voters favored Democrats by double-digits in 2006 and 2008, when the party enjoyed wave victories and seized control in Congress.
The poll was conducted April 8-11 of 900 adults – including nearly half by cell phone. It has an overall margin of error of plus-minus 3.3 percentage points. The margin of error for the 720 registered voters in the poll is plus-minus 3.7 percentage points.
While partisan lines are clear when it comes to Trump's performance and how the midterm elections are lining up, Americans are less certain about special counsel Robert Mueller's probe into potential collusion between the Trump campaign and Russia.
A plurality, 37 percent, said that indictments and guilty pleas stemming from the investigation might suggest wrongdoing by the president himself.
Yet, 36 percent or respondents, including half of independents and about 40 percent of Republicans, said they don't know enough about the case to say anything either way.