President Trump hit a record low approval in a new poll from Quinnipiac University — only 33 percent of Americans now approve of the president (margin of error +/- 3.4 percentage points). Buried in that poll is one sign of where he's losing that support: For the first time, the poll showed Trump with a negative net approval rating among white Americans without a college degree.

Because of their stalwart support of Trump, especially as opposed to their college-graduate peers, whites without college degrees (or "blue-collar whites" or "working-class whites") became an obsession during the presidential election. Indeed, whites without a college degree have sharply shifted Republican over the last two presidential election cycles.

But last week, that support slipped. The poll, conducted July 27 through Aug. 1, showed that only 43 percent of non-college white Americans say they approve of Trump, compared to 50 percent who disapprove, yielding a net approval of minus 7 points.

The margin of error for this demographic in this new poll is 6.5 percentage points, according to Quinnipiac, so it is possible that his approval with the group is still slightly positive. And (standard poll-story disclaimer) this is only one poll. Other polls might show somewhat different readings.

But the important thing here is not so much the latest readout as the trend in this polling. And a look at Trump's net approval among non-college whites over time, according to Quinnipiac polls, shows a bumpy but pronounced drop since inauguration.

Trump's approval among some groups, like Democrats and nonwhites, has been in the basement for his entire presidency. For his total approval to fall, then, the decline would have to come from demographic groups that have more room for his approval to fall.

Republicans are another group. And once again, their support for Trump is down since inauguration. In this poll, their net approval of Trump is at 62 points. That's down from 78 in the first Quinnipiac poll of the Trump administration (the margin of error among Republicans in this new poll is 6.9 points).

All of that helped push Trump's approval to a record low in this poll.

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