Washington (CNN) The immigration and government shutdown cliffhanger gripping Washington is a symptom of a broader reality: American politics is being held hostage to three nation-changing elections -- one past and two that are yet to come.

President Donald Trump, on a perpetual victory lap over his dramatic 2016 triumph, is locked into the hard-line positions on immigration on which he built the foundations of his historic campaign.

Congressional Democrats, hoping for a vote tsunami in midterm elections this fall, are being driven on by a raging anti-Trump grassroots voting base as they seek to shield nearly 800,000 undocumented immigrants brought illegally to the United States as children. But as they consider withholding support for government funding to leverage an immigration deal, Democratic leaders must balance pressure from progressives with the needs of vulnerable red state Democrats vital to their hopes of recapturing the Senate and who risk being branded by GOP foes as friends of "amnesty."

Then there are Democrats who scent a chance to stand firm on immigration to woo 2020 primary voters, who will pick who will duel an apparently weakened President for the White House.

One potential candidate, Sen. Cory Booker of New Jersey, put on an impassioned show in the Senate Judiciary Committee Tuesday, skewering Homeland Security Secretary Kirstjen Nielsen for saying she did not recall Trump using the word "shithole."

"I've got a President of the United States whose office I respect, who talks about the countries' origins and my fellow citizens in the most despicable of manner. You don't remember. You can't remember the words of your commander in chief. I find that unacceptable," Booker said.

The multiple, complicated, electoral scenarios shaping the behavior of top players in the Deferred Action for Childhood Arrivals program debate are making compromise on an issue that is central to the DNA of both parties and repeatedly defies congressional action even more difficult.

The standoff reveals again the polarization of two parties tracking ever further from the political center. And the excruciating process of dealing with the DACA recipients is an early sign of how the looming midterm elections, and even the 2020 race, are narrowing the political running room for big lifts on any contentious issue, whether it is the reform of infrastructure or entitlements.

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While he is clearly exercised with the immigration debate, and the potential prospect of a government shutdown, the President took time out on Tuesday to savor his achievement in 2016 -- a topic of which he never tires.

"How did I win Arkansas by so much when she came from Arkansas?" Trump marveled during a White House event on women, referring to his vanquished rival Hillary Clinton, before crowing about Michigan, which had been expected to go blue.

But more importantly, Trump is having a tough time watering down the purity of the positions on immigration that were instrumental in his political rise.

A week ago Tuesday, Trump told lawmakers that he would sign any bill they sent him. Then, two days later, he sunk a bipartisan deal to offer spending on his border wall in return for a reprieve for DACA recipients, apparently partly due to the prodding of his political adviser Stephen Miller, the ideological architect of the campaign's immigration stance.

Immigration tensions have also been immeasurably increased by Trump's reported blast at "shithole" African nations last week.

The episode is a flashback to 2016, when Trump's rhetoric won him a reputation among anti-Washington voters as a scourge of political correctness and a candidate who was quite happy to tear at racial and cultural divides for political gain. But it was also a flash forward to his 2020 re-election campaign. Since Trump made little attempt to broaden his appeal after the inauguration, he knows his best hope of winning a second term is keeping his base engaged.

CNN's Gloria Borger and Jim Acosta reported this week that Trump is convinced that despite the furor over his attack on African nations, his language will play well with his most loyal supporters.

"He didn't seem bothered by it at all. And he thinks it's going to help him politically, or might," one GOP source told Acosta.

Fretting Democrats

The Democratic grassroots is demanding principled, dramatic action by party lawmakers to save the Dreamers, especially after the congressional party declined to shut down the government in December over the issue.

"I think there is deep apprehension right now among the progressive base," said Murshed Zaheed, political director of CREDO, a progressive social change network. "Democrats have an open net, they can't chip wide right or wide left at this point. There is no room for error."

The DACA issue is trapping the Democratic leadership between pent-up frustration in the grassroots and a Senate electoral map that is weighted towards Republicans.

They must defend 10 Senate seats in states won by Trump two years ago, in many cases by wide margins over Clinton. That means incumbent Democrats in need independent and moderate Republican voters wary of the party line on DACA.

GOP consultants are salivating over the possibility of mobilizing conservatives by accusing red-state Democrats of voting to shut down the government to grant "amnesty" to undocumented migrants.

"I can't imagine (that) 2018 Democrats would want to shut down the government over that, especially when we are negotiating in good faith," said Texas Republican Sen. John Cornyn.

Democrats in this position include Sens. Joe Manchin of West Virginia, Joe Donnelly of Indiana, Heidi Heitkamp of North Dakota, Claire McCaskill in Missouri and Jon Tester in Montana.

Manchin said on Tuesday he would back a "clean" continuing resolution to keep government open this week -- even if it is not twinned with a reprieve for DACA recipients.

Ten is also the number of Democratic votes Senate Majority Leader Mitch McConnell may need to peel away to fund the government before a Friday midnight shutdown deadline, so red-state Democrats will come under intense pressure.

Still, progressives say the risk to Democrats in conservative states is overblown, pointing out that polls show an overwhelming majority of Americans back a right to residency for undocumented migrants brought to the US as children.

They also cite polls showing a potential blue wave in November, and argue that the victory of Doug Jones in the special election in deep-red Alabama last year shows the party can play all over the map this cycle.

"A confident opposition party fights for the heart and soul of their base," said Zaheed.

2020 stirs the pot

Party tensions are being exacerbated by the ambitions of Democrats positioning for the primary race that will explode after November.

Booker's theatrics gelled with his passionate approach to politics and were no doubt sincere. But it was impossible not to view them in the context of a potential presidential race since if he does run, they will quickly become part of his campaign lore. Booker has already signaled that he will not vote for a deal to fund that government that does not include a DACA fix, making it all but certain that other progressive senators that could run for President in 2020, including California's Kamala Harris, New York's Kirsten Gillibrand and Elizabeth Warren of Massachusetts will follow suit, as they did the last time a stopgap funding bill passed in December.

Speaking before Booker's performance, McCaskill bemoaned how the 2020 race was already complicating her life.

"We've got people running for president all trying to find their base, and then you've got people from Trump states that are trying to continue to legislate the way we always have -- by negotiation," she told The New York Times. "And never the twain shall meet."