Tax reform is why Republicans haven’t turned on Trump

(CNN) -- Washington Republicans have spent long stretches of the past 10 months -- their first with unified control of the federal government in a decade -- alternately contending with and rationalizing President Donald Trump's erratic behavior.

That those competing impulses should clash so dramatically, with a former top administration official standing in court on the same day long-desired tax cuts near passage, is a coincidence befitting the opportunity and peril Trump represents for his party.

Some Republicans have groused about him in private, others scolded or lamented him in public remarks; most dodged or demurred when confronted with the controversy du jour. When compelled, a few might issue censorious statements or tweet their concerns. But Trump has carried on, spitting Twitter venom at political foes (and allies he felt slighted by), seemingly oblivious to -- or actively spiteful of -- the sensitive mechanisms and relationships that typically drive policy-making on Capitol Hill.

Republicans in the Senate, and a handful in the House, have been subject to routine humiliations and insults from their President, even as his own team, including campaign officials and his former national security adviser, came under increasing scrutiny for their alleged ties to Russia.

After Obamacare repeal failed and his agenda looked to be falling apart, Trump pressed on, personally demeaning GOP officials who crossed him. Senate Majority Leader Mitch McConnell, Sen. John McCain, Sen. Jeff Flake, Sen. Bob Corker -- the list goes on -- have all come under attack. The latter pair will retire rather than seek re-election in 2018.

Though some of them have occasionally barked back at Trump, or bared their teeth, the threat of a damaging bite never materialized. If Trump was supposed to feel brushed back, or his skeptics emboldened, by Flake's broadside from the Senate floor in late October, well, he wasn't -- and they weren't.

Why?

On a personal level, we might never really know. Everyone has their own angle. But when framed more broadly, the trade-off is pretty clear. From the day he was sworn-in, Republicans knew, or hoped against hope, that this moment would come.

Now, with the Senate GOP poised to pass a generational restructuring of the American tax code -- one that will permanently slash the corporate rate by more than 40% (from 35% to 20%) and repeal the Affordable Care Act's individual mandate to buy health insurance -- their faith looks destined to be rewarded.

At what price, we don't yet fully know. Hours before McConnell announced he had the votes to move the legislation, former Trump national security adviser Michael Flynn pleaded guilty to lying, when questioned by the FBI, about conversations with Russia's ambassador. He is now cooperating with the special counsel's investigation.

One mystery bleeds into the next. The details of the final tax bill remain a bit of one, and will until the Senate makes it official and gets together with the House to hash out a single bill from their respective plans. (Or the House could simply pass the Senate version. We'll see.) However it plays out, one thing is for sure: Trump will sign whichever bill lands on his desk -- and do it with a big smile followed by a prolonged victory lap and a series of triumphal tweets.

For the Republican senators, like Flake and Corker and McCain, who have questioned the President's competence or cast him as some kind of existential threat to American democracy, the tax fight might have represented their last best chance to undermine Trump in a way that could alter the balance of power in Washington.

But in the end, they kept the course, the Mueller probe and all the rest existing as if in a parallel reality. The tax agenda, paired with Trump's pledge to pursue subsequent spending cuts, that have for decades animated the Republican establishment, proved too good to pass up. And if that meant tying themselves inextricably to Trump, and taking a political beating here and there, then so be it.

Asked last month during a Fox News interview, soon after Republicans suffered a round of bruising election defeats, if the party needed to consider distancing itself from the President, House Speaker Paul Ryan made plain the GOP calculus.

"We already made that choice," he replied. "We're with Trump."

He continued, spelling out unreservedly the terms of Republicans' pact with the President.

"That's a choice we made at the beginning of the year," he said. "That's a choice we made during the campaign -- which is, we merged our agendas. We ran on a joint agenda with Donald Trump. We got together with Donald Trump when he was President-elect Trump and walked through what is it we want to accomplish in the next two years. We all agreed on that agenda. We're processing that agenda."