President Donald Trump on Thursday morning tweeted about a recent Quinnipiac poll that found 66% of US voters thought the economy was in good or excellent shape, but the same poll also gave him low marks for mental fitness.

While most US voters in the poll (53%) thought Trump was intelligent, 69% thought he was not level-headed and 57% said he was not fit to serve as president.

The poll was carried out from Friday to Tuesday. Trump on Saturday sent a flurry of tweets in defense of his intelligence and fitness for office, wherein he brandished his personal successes to support his assertion that he's a "very stable genius."

Overall, the poll clocked Trump's approval rating at 36%, which has changed little during his first year in office. The same poll found that a plurality of voters (39%) graded Trump's first year in office as an F.

Quinnipiac said the poll surveyed 1,106 voters nationwide and had a margin of error of plus or minus 3.6 percentage points.