Trickle-down toxicity. Photo: Andrew Harrer/Bloomberg via Getty Images

Democrats entered the 2018 race with a challenge that few opposition parties have ever had to overcome: The administration they are running against has too many scandals (for their political opponents’ own good).

To the extent that party messaging matters at all in midterm elections (which are largely determined by differential turnout patterns shaped by “fundamentals”), a single, unifying narrative is more likely to connect with the electorate than a fusillade of discrete ideas. In 2016, the simplicity of the case against Hillary Clinton’s judgement (emails!) helped it register in the public consciousness to a degree that no single one of Donald Trump’s many scandals (his fraudulent university, abuse of contractors, alleged assaulting of women, mockery of the disabled, disrespect of prisoners of war, etc, etc.) ever did.

Thus, the immense volume and variety of Trump administration scandals have threatened to prevent the media from conveying a single, digestible story of Republican malfeasance. What’s worse, some Democratic strategists worried that the president’s myriad, spectacular affronts to human decency and public ethics could actually help his party — by diverting attention away from congressional Republicans’ historically unpopular plans to take health care from the poor to give tax cuts to the rich.

Thus, in May, the Democratic leadership attempted to boil the Trump era’s disparate scandals and regressive policies down into a single, overarching narrative of corruption. The president’s bizarre affinity for Russia, his appointees’ shameless self-dealing, and Paul Ryan’s proposals for upward redistribution were all products of the same sad fact: Trump’s Republican Party wasn’t “greedy, greedy, greedy” for America, but only for itself.

A new poll of 48 Republican-held congressional districts suggests this message is landing. The survey, which was commissioned by the progressive think tank the Center for American Progress (insert grain of salt here), finds that 54 percent of voters in these “light red” districts believe the Republican Party is “more corrupt” than the Democratic one, while 46 percent say the opposite. Among independent voters, 60 percent said the GOP was more corrupt.

And that sentiment appears to be translating into shifting partisan preferences: In past midterms, Republicans won these districts by an average of 14 percentage points; this new poll gives Democrats a 4-point generic ballot advantage.

But the survey’s most compelling finding might be this: The corruption message appears to resonate most broadly when integrated into a critique of the Republican agenda. When pollsters asked voters whether it was a serious problem that 53 congressional Republicans would “get an average tax cut of over $200,000 each from a single loophole they added to the tax bill at the last minute,” 75 percent of voters said that it was, indeed.

One shouldn’t accept the findings of any single poll as gospel truth — let alone, a single one bankrolled by a Democratic institution. But the fact that progressive organizations are releasing polls that flatter Democratic messaging — while their right-wing counterparts have released few surveys that do the opposite — is itself telling.

As CNN’s Harry Enten notes, left-wing groups have produced 93 percent of all partisan polls released this year — and historically, the “more internal polls put out by left-wing groups relative to right-wing groups, the better Democrats tend to do in House elections.”