(CNN) Despite a positive public front, congressional Republicans are quietly voicing frustration that President Donald Trump's big tax announcement Wednesday emanated from a disjointed process -- and lacked crucial components necessary in the push to secure the first major tax reform in more than 30 years.

Administration officials say the White House wanted to take the lead on this -- rather than wait for the Hill -- to garner headlines ahead of Trump's 100th day in office.

It will be "the biggest tax cut and largest tax reform in history of this country," Treasury Secretary Steven Mnuchin said earlier Wednesday, describing the proposal to The Hill.

House Speaker Paul Ryan put a positive spin on things during his own news conference Wednesday, noting that he saw the administration's announcement as a clear example that "progress is being made and we're moving and getting on the same page."

Indeed, House and Senate lawmakers all touted the administration's announcement and professed genuine enthusiasm for a big White House push on what will inevitably be a thorny and difficult process.

"The principles outlined by the Trump Administration today will serve as critical guideposts for Congress and the administration as we work together to overhaul the American tax system and ensure middle-class families and job creators are better positioned for the 21st century economy," Ryan, Senate Majority Leader Mitch McConnell, House Ways and Means Chairman Kevin Brady and Senate Finance Committee Chairman Orrin Hatch said in a joint statement.

But the lead-up to the release was far from a smooth process behind the scenes. The Trump administration has ruffled GOP feathers on Capitol Hill by getting in the way of legislators' efforts to fix the tax system.

"It's not tax reform," said one senior GOP aide. "Not even close."

While GOP lawmakers and aides directly involved in the process acknowledge both publicly and privately they are happy the White House is kicking into gear, none of the key players were given a heads-up before Trump announced he would be releasing his principles last week, according to multiple House and Senate GOP aides.

"We get that they want make a big show of leading the way on this, but that's not how this is supposed to work," one aide told CNN, adding that discussions between House and Senate tax writers and their administrating counterparts had been ongoing, if still far from any concrete agreement or pathway forward.

The White House defended the plan, which was presented in a single-page sheet during a briefing Wednesday afternoon.

"This isn't going to be easy. Doing big things never is," said Gary Cohn, director of the White House National Economic Council. "We will be attacked from the left and we'll be attacked from the right, but one thing is certain: I would never, ever bet against this President. He will get this done for the American people."

The topline principles Trump is releasing leave out the important signs of actual reform, not the least of which include: how to pay for it, what's the pathway through the House and Senate, where the key players off the Hill that have enormous lobbying clout stand on things, and more.

For some aides and lawmakers involved in the process, Trump's approach is being taken as a direct affront to Ryan and Brady, who spent more than a year on their tax proposal with the repeatedly stated goal of "once in a generation reform."

"It's really easy to talk about big cuts," a senior GOP aide told CNN. "We're about solutions. They aren't to that point yet, either on the policy or on the personnel level, and it's both obvious and disruptive to the process."

As the tax debate intensifies, one question above all is sure to emerge: How would the President's plan affect his own taxes?

For that, there is no answer, given his refusal to release his tax returns. Mnuchin said the President had "no intention" of releasing them now.

"The President has released plenty of information and I think has given more financial disclosure than anybody else," Mnuchin said. "I think the American population has plenty of information on it."