Modern polling usually tells us how public opinion hasn't moved. Despite last week's hailstorm of bad news, President Donald Trump's job approval rating stood virtually unchanged.
So did the president's backing from Republican elected officials in Washington. Except for Sen. Mitt Romney of Utah and a few others, GOP members of the House and Senate have either defended the president's actions concerning Ukraine and former Vice President Joe Biden or remained silent.
Yet surveys in recent days show public sentiment evolving more than Trump's steady topline would suggest. They also illuminate the potential for erosion among fellow Republicans, which could ultimately threaten the president's ability to survive a Senate trial on articles of impeachment approved by the House.
"If you're the president you have to take that seriously," says former Republican strategist Tom Davis, who once ran his party's House campaign arm. "What moves this ultimately is public opinion. These members like their jobs."
Last week's Monmouth University poll showed signs of movement within a broader portrait of stability. Buoyed by backing from 86% of Republicans, Trump's approval rating remained unchanged: 41% of Americans approved of his job performance, 53% disapproved. At the same time, the share of Republicans backing a House impeachment inquiry doubled to 16% from 8% in August.
A CBS News poll found 23% of Republicans backing an impeachment probe. In a USA Today survey, 30% of Republicans called it "an abuse of power" for Trump to ask Ukraine to investigate Biden.
Even if they haven't broken with their party's president, those Republicans pose a particular danger to Trump, who once bragged that he could shoot someone on Fifth Avenue in New York without losing support.
"The willingness to hear this out is a sign that you're not a Fifth Avenue Republican," says GOP strategist Liam Donovan.
Others susceptible to change include the roughly 15% of voters who already disapprove of Trump but don't yet back impeachment. This group consists largely of political independents, with some Democrats and a smaller number of Republicans as well.
College-educated whites — who disdain Trump but so far feel less strongly about impeaching him — represent a special vulnerability. If House Democratic investigators can persuade wavering Republicans that Trump withheld aid to Ukraine in return for a Biden investigation, observes GOP pollster Whit Ayres, "then it's a different ballgame."
Tribal loyalty in contemporary politics makes that a high hurdle. In the Monmouth Poll, for example, only 40% of Republicans said they believed Trump requested a Biden investigation even though the White House-released transcript of his call with Ukraine's president shows that he did.
"There are a lot of people who will go to the ends of the Earth to give Donald Trump the benefit of the doubt," Ayres explains.
Still, support for Trump's impeachment, not merely an inquiry, reached 50% in last week's Economist/YouGov poll. A 51% majority — including one in eight Republicans — said the Senate should remove Trump from office if the House votes to impeach him.
It will take more defections than that to shift the cost-benefit analyses of the GOP politicians whose voters will decide Trump's fate. Virtually all of them — including swing-state senators on the ballot in 2020 such as Martha McSally of Arizona, Cory Gardner of Colorado and Susan Collins of Maine — fear defections among Trump-loving Republicans at least as much as an anti-Trump wave.
"We're a long way from any Republicans being ready to vote for impeachment, even if they don't like the guy or think he's a good president," cautions GOP pollster Glen Bolger.
That may never happen. Democrats can pass impeachment articles in the House all on their own, but would need the votes of at least 19 Republican senators to convict and remove Trump from office in a Senate trial.
Yet new evidence keeps tumbling out nearly as fast as House Democrats subpoena documents and testimony from administration officials.
Today, Ohio Sen. Rob Portman broke with Republican colleagues who have excused Trump's conduct, calling it "not appropriate." Portman stopped short of supporting impeachment, saying Congress needs to be "very careful" about that step.
But the fact that mainstream Republicans entertain the discussion while watching the polls underscores Trump's heightened peril.
"I certainly wouldn't vote to impeach on the basis of what I've seen so far," says veteran Rep. Tom Cole of Oklahoma, a former executive director of the Republican National Committee. "I'm not going to rule it in or out."