WASHINGTON — President Donald Trump broke a fundamental rule of modern politics Saturday when he outlined a new plan to get his border wall and re-open the federal government: Never split your own party.

The basic idea is to give 1 million immigrants — 700,000 so-called Dreamers who were brought to the country illegally as children and 300,000 refugees facing expiration of their "temporary protected status" — a three-year shield from deportation in exchange for $5.7 billion in funding for the wall.

While Republican leaders on Capitol Hill praised his leadership, and Senate Majority Leader Mitch McConnell, R-Ky., readily agreed to bring his proposal up for a vote on the floor next week, conservatives were quick to criticize the president for offering "amnesty" to undocumented immigrants.

Trump proposes amnesty. We voted for Trump and got Jeb! — Ann Coulter (@AnnCoulter) January 19, 2019

"Amnesty encourages further illegal immigration, incentivizes the tragedy of human trafficking, and undermines our citizens' confidence in the rule of law," James Carafano of the conservative Heritage Foundation said in a statement released shortly after Trump delivered remarks on the plan from the White House. "Amnesty should not be part of any border security deal, especially given that many who today oppose a wall have publicly supported and even voted for physical barriers in the recent past."

The obvious problem for Trump is that he managed to divide his own ranks without much chance of breaking the wall of Democratic opposition to his border barrier. Congressional Democrats were quick to reject his plan.

"The president’s announcement today falls flat and includes the same wasteful, ineffective and unpopular $5.7 billion wall demand that shut down the government in the first place," Rep. Joaquín Castro, chairman of the Congressional Hispanic Caucus, said in a statement. "Further, the President’s offer is similar to previous proposals that included temporary DACA protections and that the President killed last Congress."

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The big political question is whether Trump's latest gambit will give traction to his ongoing argument that Democrats have been intransigent and should now shoulder the blame for the longest government shutdown in history. Polls have consistently shown that most Americans blame him — he once said he would be "proud" to allow a lapse in funding for federal agencies in order to force Democrats to capitulate on the wall money — and that only about a third of them see Democrats as the culprits.

Trump's politics have always been unorthodox — he and his supporters view that as an asset in Washington — and, by putting forward a plan that angers some of his base, he may be hoping more swing voters see Democrats as needlessly intractable and move toward his position in this fight.

Trump called for bipartisanship Saturday, even as he painted the Democratic Party as a hostage of its left-most fringe.

"These problems can all be solved but only if we have the political courage to do what is just and what is right," he said, as he called for the two sides to "come together, listen to each other, put down their armor, build trust, reach across the aisle and find solutions."

Rep. Gerry Connolly, D-Va., said "it's possible, but unlikely" that the sweeteners of a temporary extension of the Deferred Action for Childhood Arrivals (DACA) program and the window for certain immigrants who have "temporary protected status" (TPS) will make it easier for Trump to sell his case that Democrats are to blame for the shutdown.

"He created the DACA and TPS messes and is dangling a temporary fix as a bargaining chip? — $5.7 billion or I deport them," Connolly said.

Indeed, Trump sought to end the Obama-era DACA program and crack down on TPS for certain immigrants, but courts have thus far blocked him.

Stacey Plaskett, the Democratic delegate from the Virgin Islands, said Democrats have to be smart in their response to Trump's proposal.

"I'm concerned that my party speak clearly for Americans to understand that we've been trying to talk about DREAMers, TPS, border security, etc., for the last two years, but when Trump controlled Congress with Republicans in power, none of this, including border security, was of primary importance," she said in a text message to NBC. "Then, all they were concerned about was tax cuts for the rich and getting rid of affordable health care."

Whether his new plan earns him more support from independents in the fight over the shutdown and the wall remains to be seen. But it is highly unlikely to move many Democratic voters or their elected representatives, who have been united in their demand that he open the shuttered federal agencies without money for the barrier.

If he finds himself offering more to Democrats to re-open the government later on — or backs down from the wall — he will have caused himself more pain than necessary by issuing this plan. If his proposal ends up shifting public opinion enough to move Democratic votes, that may take time.

So, as a practical matter, the government is no closer to opening, and Trump is no closer to getting cash for the wall.

Often, deal-making requires a president to disappoint a segment of his own base to attract support from a portion of the other party. But in this case, Trump has created a split within his own party without finding a way to divide Democrats.

That's certainly a non-traditional approach to politics, but it may not be a winning one.