WASHINGTON — As he fought for political survival in 2016, Sen. Pat Toomey told Pennsylvania voters he was so uncomfortable with Republican Donald Trump that he didn’t know whether he would support his own party’s nominee for president.

Toomey said he saw “two very badly flawed candidates” and vowed to be an “independent voice,” no matter who won. Despite repeated questions, he didn’t disclose that he would vote for Trump until hours before polls closed.

Now, Toomey’s promises of independence are facing high-stakes scrutiny.

With the U.S. House moving quickly toward impeaching Trump, possibly before year’s end, senators are bracing to sit as the jury. Most Republicans are sticking with the president, but they face increasing pressure in the face of damning revelations and, next week, the start of televised House hearings.

Toomey has said Trump’s pressure on Ukraine, including withholding desperately sought U.S. aid while pressing for a damaging investigation into Democrat Joe Biden, was “inappropriate” but not impeachable. He reiterated that stance in an interview Wednesday.

“None of it has changed my fundamental view on this,” Toomey said of recent revelations. “I think there needs to be a very high bar for removing a president from office. It has never happened in the history of the republic, and I think this president has made errors of judgment and he has said and done things that I don’t agree with, but I have yet to see something in my mind as a high crime or misdemeanor that warrants overturning the results of the last election.”

His stance makes Toomey one of few Senate Republicans to have said anything even mildly critical of Trump’s conduct with Ukraine. But he has saved harsher words for House Democrats, accusing them in a recent statement of “disgracefully breaking with” bipartisan precedent on impeachment inquiries.

To his critics, Toomey’s focus on Democrats shows he has not lived up to his pledge to be independent

“I don’t understand why somebody who says, ‘I’m not going to be a rubber stamp’ has continually rubber-stamped a lot of things ... and refuses to even acknowledge that something might be wrong,” said Philadelphian Vashti Bandy, a founder of the grassroots liberal group Tuesdays with Toomey, which protests outside his offices every week. “It makes me think he’s more interested in protecting his own job than he actually is in serving the country.”

Toomey pointed to numerous instances in which he has criticized Trump’s behavior, and several cases, most prominently on trade, in which he has opposed Trump policy goals, including a highly touted trade deal with Canada and Mexico.

“When it comes to being willing to publicly disagree with the president on policy and push back, there are very few Republican senators who have done as much as I have,” he said. “People, I know, choose for their own purposes to ignore these things, but it doesn’t mean they don’t exist.”

He added that a senator’s independence “could never meaningfully be defined” by one vote, even one as big as impeachment.

Toomey’s career has had unusual intersections with the issue.

The GOP impeachment of President Bill Clinton raged during his first run for the U.S. House, in 1998. He refused then to take a position on that fight. (His Democratic opponent also avoided the question for most of the election.)

Years later, Toomey would challenge and then replace one of the few GOP senators who broke ranks to acquit Clinton — Sen. Arlen Specter.

Specter’s son Shanin said his late father’s experience showed that lawmakers should keep an open mind (though he did not directly name Toomey).

“When it comes to the core responsibilities of a member, such as a resolution on the use of force or an economic crisis or a Supreme Court confirmation or an impeachment trial, if a member does not put aside party and vote his conscience, he doesn’t belong there,” said Specter, a Center City lawyer who has donated to Democratic campaigns, including Biden’s.

He added that his father “regarded himself as a juror, and he did not say and would not have said that the evidence as it was being developed was or was not sufficient to warrant conviction.”

Toomey, who effectively chased Specter out of the GOP — Specter became a Democrat rather than face Toomey in a 2010 primary — said that he remains open to new facts but that he is responding to reporters’ questions about the evidence so far. Senate Republicans note that they don’t have all the information because the House is still conducting the investigation and hasn’t brought formal charges.

Charlie Dent, a former GOP congressman from Allentown and a fierce Trump critic, said Republicans can never satisfy Trump’s opponents.

“They’ll never do enough to please the Never Trumpers and they’ll never be seen as loyal enough to the Trump sycophants,” said Dent, who represented Toomey’s hometown.

Toomey doesn’t face immediate political pressure: He isn’t up for reelection until 2022. His vows of independence played well in the Philadelphia suburbs in 2016, allowing him to hold his own in an area that has since become a GOP wasteland. If Toomey runs again, being tied to Trump could damage him, but he also can’t afford to alienate Republicans who fervently support the president.

Toomey, known for choosing his fights carefully, has criticized some of Trump’s most divisive behavior.

He released statements condemning the president’s tepid response to the neo-Nazis who marched through Charlottesville, Va.; and the Trump rally chants of “send her home!” targeting Rep. Ilhan Omar (D., Minn.), among other examples.

After Trump’s infamous news conference with Russian President Vladimir Putin, a Toomey statement called Trump’s “blindness" to Putin’s hostility "very troubling.”

Like many Republicans, Toomey has also pushed back on foreign policy, including Trump’s recent decision to pull U.S. troops out of Syria and abandon Kurdish allies. And he opposed Trump’s effort to divert military funding to his border wall.

Toomey’s most persistent and vocal criticism of Trump, though, has been on the issue at the core of his political career: free enterprise. He has repeatedly blasted Trump’s trade policies and tariffs in news conferences, television appearances, Senate hearings, and speeches. He has tried to round up GOP support to reverse those policies, to little avail.

But he has picked his spots, helping him avoid the Trump backlash that has crushed other Republicans, such as former Sen. Jeff Flake of Arizona, said David McIntosh, president of the Club for Growth, the business-friendly group Toomey once led. McIntosh said that approach has allowed Toomey to remain in position to work with Trump on issues on which they agree.

And on the vast majority of policy debates and nominations, Toomey has voted with Trump and fellow Republicans.

Trump’s pushes to cut taxes and repeal the Affordable Care Act aligned with the fiscally conservative approach Toomey championed since his days as a House member in the early 2000s. He helped write and pitch both of those proposals.

Bandy, of the protest group, said Toomey’s statements sometimes pleasantly surprise her, but aren’t enough. She argued that he should push back on harsh Trump policies with the same force he puts behind his priorities.

“I stand on a street corner every Tuesday and I make a statement. That is the power that I have,” said Bandy, a writer. “Sen. Toomey is a U.S. senator. He has power within his caucus.”

Toomey never did take a stand on Clinton’s impeachment. The House voted before new lawmakers were sworn in, so Toomey didn’t read all the materials, knowing he would never have a formal say, he said at the time. The Democratic congressman he was replacing, Paul McHale, broke ranks and supported the impeachment of a president from his own party.

Speaking to high school students just before Christmas in 1998, Toomey said McHale “studied the articles very closely and he voted his conscience, which was the right thing for him to do.”