Republicans, confident they've found the votes to pass a massive tax overhaul, entered the next phase of their effort Sunday, attempting to sell the plan to a public that polling suggests is deeply skeptical.

GOP leaders argued that the tax bill — the final version of which was unveiled Friday — is aimed primarily at helping the middle class, brushing aside nonpartisan analyses that show the bulk of the legislation's benefits would go to the wealthy and to corporations.

“This is a very large tax cut for working families,” Treasury Secretary Steven Mnuchin told CNN. He said some upper-income families, particularly in blue states, would actually see their taxes go up because of the reduction of the state and local tax deduction under the plan.

The sales pitch is trying to turn public opinion in favor of a $1.46 trillion Republican bill that centers on a massive tax rate decrease for corporations and a dramatic reduction in the estate tax, which is paid only by a fraction of the wealthiest American families.

Most Americans would see their overall tax burden reduced under the bill during its first few years of implementation, but the plan's long-term implications for the middle class are more complicated, depending both on an individual family's circumstances and decisions that won't be made for years.

The size of individuals' tax cuts will vary widely, due in large part to changes that the measure would make to the tax code's complicated system of tax deductions. The bill would double the “standard” deduction used by many middle-class taxpayers while also eliminating or reducing some other deductions frequently used by those who itemize their returns.

The plan schedules many of these individual-side tax cuts to expire in eight years, though Republicans say they expect a future Congress to extend these cuts before they sunset and that, as such, they should be considered permanent.

The bill would also raise revenue by eliminating the Affordable Care Act's individual mandate, which the Congressional Budget Office estimates will lead to 13 million fewer Americans having health insurance a decade from now.

Americans have been skeptical of the promises the GOP is making about the bill. Polling has consistently found approval ratings for the bill at below 35 percent, and a CBS poll from last week found that 76 percent of Americans believe its biggest benefits will go to the largest corporations.

Congressional Republicans have started their uphill climb to persuade Americans otherwise, touting the broad benefits they expect as a result of the large corporate rate tax cut and dismissing claims that the bill will balloon the deficit.

“This will benefit hard-working American families, people in the lower income tax brackets, and everybody in every tax bracket will see a tax cut,” Sen. John Cornyn (R-Tex.) told ABC News.

Confronted by a report from the International Business Times that some Republican lawmakers inserted last-minute changes that would personally enrich them, Cornyn said: “Our Democratic colleagues simply refused to participate in the process — we probably could have made it better if they had.”

But not everyone is convinced, including members of their own party. “Do I think they could have done better for the middle class? I do,” Gov. John Kasich (R-Ohio) said on NBC's “Meet the Press.”

While the tax debate has consumed Congress, there has been scant progress toward a spending deal. Current federal spending authority is set to expire Friday, and a partial government shutdown will ensue if Congress does not act to extend it.

House Republican leaders filed a spending bill last week that would temporarily extend funding for most government agencies at current levels until Jan. 19, while providing longer-term military funding at higher levels — $650 billion through Sept. 30. But that bill is considered dead on arrival in the Senate, where Democrats can block it because of the chamber's 60-vote filibuster threshold.

To cut a long-term spending deal, Democrats are pushing for an equivalent increase in both defense and nondefense funding above the spending caps set under a 2011 budget agreement — one similar to agreements reached in 2013 and 2015 to raise the caps for the following two years. But bipartisan negotiations that have been open for weeks have yet to produce an accord.

Democrats railed against the House GOP gambit last week. Senate Minority Leader Charles E. Schumer (D-N.Y.), in floor remarks Thursday, called the proposal “a spectacle, a charade, a sop to some militant, hard-right people who don’t want the government to spend money on almost anything.”

He added: “And it is a perilous waste of time as the clock ticks closer and closer and closer to the end of the year.”

The spending talks are suffused with other issues. For instance, Democrats and some Republicans want legislation providing legal status to “dreamers” — immigrants brought to the United States illegally as children — to be attached to the year-end deal.

Sen. Susan Collins (R-Maine) struck a deal with Trump and Senate Majority Leader Mitch McConnell (R-Ky.) to provide subsidies for the Affordable Care Act health insurance marketplaces in return for her vote on the tax bill.

The Children's Health Insurance Program expired Sept. 30, and states have been warning for weeks that coverage could be threatened if Congress does not reauthorize it soon.

And a key surveillance authority used by U.S. intelligence agencies to monitor noncitizens abroad expires Dec. 31, prompting fears of a lapse in national security.

Even if a bipartisan agreement is reached on some or all of these issues, the timeline is tight: The House is not expected to vote on its spending bill until Wednesday at the earliest, leaving little time for the Senate to take that bill, amend it, and send it back to the House. Any hiccup could mean a breach of the Friday shutdown deadline.