There’s some debate over what metric provides the best assessment of the political future of President Trump. Is it the strength of support in his base? Is it the opposition from Democrats? Is it how independents feel? Is it how Republicans feel?

I happen to subscribe to a mix of the latter two metrics. If Republicans waver on Trump, that could inspire members of his own party to speak out more strongly against Trump before the House primaries next year. If independents continue to be unusually skeptical of him, that could make Republicans in tough House races bail on him even more rapidly. Trump’s broad unpopularity means that there may be more close races than we might have expected a few months ago.

A new Quinnipiac University poll released on Wednesday suggests that, since a surge in opposition early in his presidency, strong opposition to or support for Trump’s job performance has been fairly steady — suggesting no great erosion that would cause increased nervousness about those elected officials yet.

On the biggest shadow being cast over Trump’s presidency — the ballooning investigation of Russian meddling and how Trump has responded to it — the poll offered some starkly bad news for the president and his party.

In controversy after controversy, Republican lawmakers have defended President Trump. His disclosure of highly classified information may be too far. (Jenny Starrs/The Washington Post)

Remember that 88 percent of Republicans voted for Donald Trump in 2016, a smaller percentage than Mitt Romney earned four years before, but the vast majority of his party’s voters. Compare that 88 percent with Republican support on a slew of questions about the firing of FBI Director James B. Comey and the investigation into possible Trump campaign collusion with Russian actors.

On the firing, only a bit over a third of the country approves — including 73 percent of Republicans.

It gets worse from there. In the letter he sent to Comey to terminate his position, Trump added an unusual line claiming that Comey told him multiple times that he himself wasn’t under investigation. Only 31 percent of Americans — and only 54 percent of Republicans — believe that.

Why? Well, in part because most Americans (and a decent chunk of Republicans) don’t think that Trump is honest.

Most Americans also believe news reports that Trump asked Comey to drop the investigation into his former national security adviser Michael Flynn. Even a quarter of Republicans believe that report.

Asked if they believed Comey was fired because Trump lost confidence in his performance or, instead, that it was to try to disrupt the Russia investigation, most think it was the latter, though only about 14 percent of Republicans do.

A key problem for Trump is that, while Republicans felt as though he was within his rights to fire Comey, a third of them disapprove of how he handled the firing. Only 55 percent approve — compared with only a quarter of Americans overall.

Almost half of Americans think that it was an abuse of his power to fire Comey.

But this isn’t the only problem area for Trump, of course. More than 60 percent of Americans are very or somewhat concerned about reports that Trump revealed classified information in a private meeting with Russian officials. A quarter of Republicans agree.

When asked if Trump is abusing his power overall — not just in the Comey case — more than half of Americans agree. That includes only 12 percent of Republicans, presumably overlapping substantially with that 12 percent that didn’t vote for him. But 46 percent of independents voted for Trump in 2016, and more than half now think he’s abusing his power.

In fact, on every single question we’ve highlighted in Quinnipiac’s poll, independents hold a position closer to the Democratic position than the Republican one (save on the “abuse of power to fire Comey” question, where independents were midway between the parties).

Quinnipiac asked about continuing the investigation into Russian meddling in several ways. Was it important that the next FBI director should continue that investigation? Eighty percent said, yes, it was very or somewhat important — including 64 percent of Republicans.

Did Americans support an independent commission? Yes, 73 percent did — including 45 percent of Republicans.

A special prosecutor, similar to the one appointed last week by the deputy attorney general? Yes, two-thirds of Americans support that appointment, including a third of Republicans.

In short? Republicans stand by Trump, but the undercurrent of concern about the ongoing investigations is often broader than the support the party showed him during the last election cycle. Independents tend to align more with Democrats when considering the question of how Trump’s behaved on the matter.

We’re often quick to point out warning signs that may amount to nothing. But when there’s a warning sign, it’s still generally worth pointing out. And for Trump and his party, this poll is a warning sign.