William F. B. O'Reilly Portrait of Newsday/amNY columnist Bill O'Reilly (March 28,

William F. B. O'Reilly is a consultant to Republicans.

Donald Trump, to the best of my knowledge, has never shot anyone along New York City’s Fifth Avenue. But his boast that he could do so and not lose core supporters has so far held up.

Thursday’s Senate Intelligence Committee hearings are going to test that contention like never before. And they’re just the beginning of what could be a make-or-break summer for the Trump presidency.

Former FBI Director James Comey’s testimony — including his opening statement released Wednesday — alone won’t budge Trump’s rock-ribbed apologists. Comey is distrusted because of his handling of matters during the 2016 campaign, polls suggest. But if news reports are true — and they haven’t been denied — that the president also asked National Intelligence Director Daniel Coats and CIA Director Mike Pompeo to lean on Comey to drop the FBI’s Russia investigation, it’s going to be a tough pill to swallow even for the Kool-Aid drinkers.

It shouldn’t matter how the president is perceived by his political base. But it means everything in reality: As long as Trump retains significant grass-roots Republican support, just 20 or 25 percent, members of Congress won’t break with him en masse. Doing so would spell political suicide for them in 2018, through primary challenges and/or Republicans bass fishing instead of voting during the midterm elections (the same may happen if this Congress can’t pass tax reforms). Republican support for Trump hovers at around 80 percent right now, with somewhere between a quarter and half of that hard core support.

Comey’s testimony should make sensational TV. But the things to really watch are Trump’s GOP poll numbers following his appearance. They’ll tell you whether Trump will have allies on Capitol Hill much longer.

Another key indicator: How many Republicans believe there’s anything to the Russia inquiry at all. In late March, despite overwhelming evidence to the contrary, just 13 percent of Republicans surveyed by CBS News said they believed Russia meddled in the 2016 election. In an ABC News poll released Wednesday, 61 percent of Republicans said they believed Trump fired Comey “to protect himself” rather than for the good of the country. Sixty-one percent of Americans overall believed Trump’s motivation was self protection, the survey said.

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If Coats and Pompeo testify that Trump indeed asked them to weigh in with Comey on the Russia investigation, what will happen to those numbers?

Maybe nothing. We simply don’t know.

The strangest thing about this whole Russia mess, though, isn’t the Comey firing, nor is it Attorney General Jeff Sessions’ self-recusal in the investigation or former National Security Adviser Michael Flynn’s abrupt firing, it’s how the Trump administration has continued to posture itself toward Russia while this is all going on. It’s downright bizarre.

How is it possible that discussions about sanction relief for Russia, including the return of Russian properties allegedly used for spying in the United States, continue as even more evidence mounts that Russia was knee-deep in trying to manipulate our elections?

How is it possible that Trump omitted the key sentence in his prepared NATO speech last month that would have reassured the world about America’s military commitment to an alliance created to protect Western Europe against Soviet-Russian encroachment?

Why on earth has Secretary of State Rex Tillerson’s State Department been seeking to ease sanctions on Russian oil production as all this plays out? Does the administration truly not care about how this all looks, or are there larger forces at play?

I get political loyalty. I cried when Richard Nixon resigned the night before my 11th birthday. But, as with Watergate, the questions are really starting to pile up for this administration. Patriotic Republicans can’t ignore them any longer.

William F. B. O’Reilly is a consultant for Republicans.