By Jeremy Diamond and Kevin Liptak, CNN

(CNN) -- President Donald Trump on Wednesday unveiled a Republican framework for tax reform that calls for sweeping tax cuts and a simplification of the tax code, framing the effort in a speech as a historic opportunity.

"This is a once-in-a-generation opportunity, and I guess it's probably something I could say that I'm very good at," Trump said during remarks in Indiana. "I've been waiting for this for a long time. We're going to cut taxes for the middle class, make the tax code simpler and more fair for everyday Americans. And we are going to bring back the jobs and wealth that have left our country and most people thought left our country for good."

Trump in recent weeks has sought to crank up public pressure on the need for sweeping tax reform. In Indianapolis, he offered specific numbers to back up his calls for the biggest changes to the tax code in decades.

He called for reducing the personal income tax brackets from seven to three (12%, 25% and 35%), doubling the standard deduction for married and single filers (to $24,000 and $12,000 respectively), slashing the corporate tax rate to 20% and eliminating the estate tax -- among other proposals.

Trump sought to give the Republican-crafted framework a populist touch, framing the tax reform proposal as a boon for the middle class, American workers and American manufacturing.

The President said his tax cut proposal wouldn't help the country's wealthiest taxpayers, like himself, as he promised to strip away tax breaks and loopholes.

"It's not good for me, believe me," Trump said.

The claim was impossible to verify, though, as Trump has refused to release his tax returns. Trump is the first president in four decades not to do so.

Trump said that while wealthy, "well-connected" people could "call me all they want, it's not going to help," saying he was "doing the right thing."

The President's tax reform framework proposes cutting the top income tax bracket from 39.5% to 35%, though the plan gives congressional committees latitude to create a fourth, higher income tax bracket.

While Trump claimed parts of his tax proposal would hurt his wallet, he seemed sure the plan would bolster his popularity.

"What is good for me, not only as President and legacy, what is good for me is if everything takes off like a rocket ship," Trump said. "Like it should have for 20 years. That's good for me. That's good for everyone. And that's what I think is going to happen. And a lot of very wealthy people feel the same way, believe me."

Still, while the President focused on the benefits the tax proposal would deliver to middle class Americans, he made clear it would also be a boon for big business.

Beyond slashing the corporate tax rate to "no higher than 20%," Trump's proposal also offers write-offs for companies that move their manufacturing plants to the US and would incentivize the repatriation of "trillions" of dollars in US companies' profits stashed in tax havens overseas.

"Our framework will stop punishing companies for keeping their headquarters in the United States. We're punishing companies under our codes for being in the United States," Trump said. "When our companies move to other countries it's our loyal American workers who get hurt."

Trump said his business-friendly policies would lead to increased wages and economic gains in the US. The GOP framework would also cap the tax rate for small businesses at 25%, Trump said.

The framework is the result of months of closed-door discussions between top Trump administration officials and Republican congressional leaders, but Trump has signaled in recent weeks that he is hoping to win some Democratic support for his proposal.

Trump's trek to Indiana on Wednesday was the third time he has pitched tax reform in a red state that is home to a vulnerable Democratic senator, this time Sen. Joe Donnelly, who joined Trump for the speech.

Trump took the opportunity to turn up the heat on Donnelly, who is up for reelection in 2018, warning him to support tax reform, or else.

"If Sen. Donnelly doesn't approve it -- because you know he's on the other side -- we will come here, we will campaign against him like you wouldn't believe," Trump said, pointing at Donnelly in the audience before suddenly offering a wide grin. "I think they're going to approve it, I think we'll have, actually I think we'll have numerous Democrats come across, because it's the right thing to do."

Trump added that "tax reform has not historically been a bipartisan issue," drawing on the example of the Reagan tax cuts which were passed with significant Democratic support as he said he hoped Democrats would join in supporting the reform effort.

Trump drew on the stories of ordinary Americans as he made his pitch, referring to a seventh-generation farmer to call for a repeal of the estate tax, drawing on the story of a small business owner as he calls for tax cuts and pulling from the experiences of an IT worker whom Trump said has seen firsthand the damage of the US' high corporate tax rate.

The GOP proposal, being presented jointly by the White House, House Ways & Means Committee and Senate Finance Committee, calls for reducing income tax rates to three brackets of 12%, 25% and 35%, but leaves the income ranges for those brackets up to tax committees, according to a copy of the Republican framework obtained by CNN. The proposal also gives committees the flexibility to create a fourth bracket that could potentially eliminate a potential tax cut for the wealthiest Americans.

The proposals also calls for doubling the standard deduction to $24,000 for married couples and $12,000 for single filers.

The framework also calls for slashing the corporate tax rate to 20%, though Trump has for months said he would like to see the 35% rate brought down to 15%. Trump sought to justify the shift on Wednesday, saying that he only floated 15% as a negotiating tactic.

"I wanted to start at 15 to get there," Trump said.

Trump's push on tax reform comes on the heels of his latest in a string of stinging defeats on health care reform, with Senate Republicans repeatedly failing to string together 50 votes to replace Obamacare.

The White House is now aiming to push tax reform through Congress by the end of the year.

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