Senate Majority Leader Mitch McConnell (R-KY), speaks to reporters about the proposed Senate Republican tax bill, after attending the Senate GOP policy luncheon, at the US Capitol.

Republicans are about to pass a tax plan that most people don't like, pushed by a president they like even less.

That's the bleak situation the GOP finds itself in to close out 2017 as a pair of new polls demonstrate the unpopularity of both the party's standard bearer and its chief legislative agenda item setting up what could be a dismal midterm election cycle for Republicans.

A CBS News poll out Thursday found that over half of Americans oppose the GOP's tax cut plan and 40 percent oppose it strongly. Republicans generally support the plan but only a third of them believe their own taxes will decline under the proposal, which is focused on a big cut in the corporate rate.

Overall, 41 percent believe their own taxes will rise and just 22 percent think they will go down. Large majorities believe the plan will help corporations and the wealthy, while just 31 percent think it will help the middle class.

President Donald Trump's numbers are even worse.

The latest Pew Research Center poll found the president's approval rating at a new low of just 32 percent, making him the least popular president in modern American history at this point in a first term. The ongoing Russia probe is taking a major toll on Trump, with 59 percent of Americans believing that improper contact definitely or probably took place during the campaign.

The numbers highlight a stark reality for Republicans heading into the midterm election year. Unless views of Trump and the party's legislative agenda change dramatically over the next 11 months, the party is likely to lose significant ground next November with control of both the House and Senate potentially in play.

And fresh obstacles remain this year. Republicans in Alabama on Tuesday may elect an accused child molester, Roy Moore, as their next senator, putting party leaders in Washington in the deeply uncomfortable position of seating a man faced with credible accusations from multiple women. Or they could anger Trump and his nationalist base by attempting to block Moore from taking his seat.

The alternative is also bleak for Republicans. Should Democrat Doug Jones win in deep-red Alabama, it would spare the party the nightmare of welcoming Moore to Washington but it would not augur especially well for the GOP heading into the midterms. Republicans also face the prospect of a government shutdown on Dec. 22 unless they can make a deal with Democrats on a longer-term funding bill.

Democrats have significant leverage to demand increased domestic spending and a deal on the Deferred Action for Childhood Arrivals program, which protects immigrants who came to the United States as children.

Republicans could insist on keeping DACA out of a deal and limiting nondefense spending increases but could then get blamed for a shutdown, given that they control both houses of Congress and the presidency. If Trump and the GOP back down on DACA and White House demands for border wall funding, they will likely anger the America First base.

On the tax plan, Republicans are hoping that the corporate rate cuts will eventually lead to faster growth and bigger paychecks, increasing the bill's popularity over time. But that's not likely to materialize at least until 2019. And in the meantime, Democrats will relentlessly hammer the tax bill as a giveaway to the rich that ultimately raises middle-class taxes while blowing up the deficit.

The plan could be especially harmful to Republicans in wealthier suburbs where taxpayers could lose most if not all of their cherished deductions for state and local taxes.

Then there is the matter of the party's 2018 agenda.

The White House signaled this week that Trump would like to roll out an infrastructure package in January. That could be a popular proposal. But it has a deeply uncertain path to enactment, given the party is already adding $1.5 trillion to the deficit with the tax cut and Republicans are not likely to be enthusiastic about more spending.

And Democrats are not likely to get on board with a GOP effort that focuses on incentives for the private sector to pursue infrastructure projects rather than having the government spend the money directly.

Beyond the infrastructure plan, House Speaker Paul Ryan has suggested he wants to pursue an entitlements overhaul next year. This puts him at odds with Trump, who has pledged to protect the popular Social Security and Medicare programs. And it is perhaps the least popular thing Republicans could do heading into the midterms.

Ryan may be betting that 2018 will be the last chance he has for a while to enact sweeping changes while Republicans enjoy total control of Washington. Entitlement changes has long been one of his chief goals. If Ryan isn't betting that the GOP could lose one or both houses of Congress in 2018, he may be worried that the White House will be even less interested in entitlement changes in 2019 as a potential Trump re-election campaign nears.

But whatever the reasoning, Ryan appears set on doing what would appear impossible: settling on a legislative agenda for next year that is even less popular than the tax plan the GOP appears poised to enact later this month.

—Ben White is Politico's chief economic correspondent and a CNBC contributor. He also authors the daily tip sheet Politico Morning Money [politico.com/morningmoney]. Follow him on Twitter @morningmoneyben.