If there was one thing that threatened to prevent Donald Trump from becoming President Trump, it was his temperament. And if there was one issue about which Americans on both sides remained concerned about Trump, it was his relationship with Russia.

A new Washington Post report that Trump shared highly classified information with two senior Russian officials in the Oval Office last week lends legitimacy to both of those concerns. To many, it would seem a pair of their worst fears come true, all at once.

As The Post's Greg Miller and Greg Jaffe report, Trump provided classified details of an Islamic State plot gleaned from an intelligence-gathering alliance in the Middle East that is secretive even among allies and within the U.S. government. And he did so in a way that officials think Russia, whose goals in Syria are often at odds with the United States', may be able to figure out who the partner is, jeopardizing a key source of intelligence.

The White House isn't really denying it, with national security adviser H.R. McMaster saying, "At no time were any intelligence sources or methods discussed, and no military operations were disclosed that were not already known publicly.” The Post's report didn't say those things were discussed.

During the 2016 campaign, as many as two-thirds of Americans questioned whether Trump had the temperament to be president. And that concern seemed to seep well into his early months as president, with Trump still tweeting erratically and spewing falsehoods. As I wrote last month:

President Trump's biggest liability on the 2016 campaign trail was almost always his temperament. An October Washington Post-ABC News poll showed 64 percent overall — and 3 in 10 Republicans — said Trump didn't have the right personality and temperament to be president.
The first three months of the Trump administration have done nothing to disabuse them of this belief. A new Pew Research Center poll shows 63 percent of registered voters say that Trump is "too impulsive" in making important decisions. And that includes 30 percent of Republicans and Republican-leaning independents.

A Fox News poll conducted at the tail end of the 2016 election also drilled down on this issue in a way that I think is telling. It asked two questions: whom people trusted to defeat ISIS, and whom people trusted more on making decisions with nuclear weapons.

Trump led by nine points on the ISIS question. But when it came to nukes, Hillary Clinton led by 22 (!). Again, it seemed to come down to Trump's temperament -- and the worst-case scenario when it came to Trump's temperament.

Here's ISIS:

And here's nukes:

And if there was one foreign policy issue that concerned people when it came to Trump, it was Russia. As his Syria strikes have received a thumbs-up from voters and his posture toward North Korea takes shape, polls have shown that Americans are still pretty worried about Trump's relationship with Moscow and want to know more.

A Quinnipiac University poll a couple of weeks back showed seven in 10 Americans were either "very concerned" (46 percent) or "somewhat concerned" (24 percent) about Trump's relationship with Russia. Even 40 percent of Republicans were at least "somewhat concerned."

Those concerns -- on both Russia and Trump's temperament -- don't seem to be going anywhere.