President Trump, in a televised White House address Saturday, offered Democrats a compromise package on immigration in an effort to end the nearly monthlong partial government shutdown -- although some prominent Democrats were dismissing the olive branch as a "non-starter" before Trump even spoke.

Trump announced that he was prepared to back a three-year extension of protections for 700,000 immigrants who came to the country illegally as children and were shielded from deportation under the Obama-era Deferred Action for Childhood Arrivals (DACA) program. This, in exchange for the $5.7 billion he has requested for a barrier on the southern border with Mexico.

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"Walls are not immoral," he said, adding that a wall "will save many lives and stop drugs from pouring into our country."

"This is not a concrete structure from sea to sea," he said, addressing some previously expressed concerns about the so-called "wall." "These are steel barriers in high-priority locations."

The offered deal would also extend protections for 300,000 recipients of the Temporary Protected Status (TPS) program -- which protects immigrants from designated countries with conditions that prevent nationals from returning safely.

"Our immigration system should be a source of pride, not a source of shame as it is all over the world," Trump said, before urging politicians to "take off their armor" and find solutions.

It would allocate $800 million for drug detection technology to secure ports of entry, 2,750 new border agents and law enforcement professionals, and 75 new immigration judges to reduce an immense backlog of asylum requests.

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He said that all his proposals have been supported by Democrats before.

He spent much of the address talking about the dangers that an open border presented, describing a "very wide and open gateway for criminals and gang members to enter the United States." However, he also teased the possibility of future, broader immigration reform if his proposals were accepted by Congress.

"If we are successful in this effort, we will have the best chance in a long time at real, bipartisan immigration reform, and it won’t stop here, it will keep going until we do it all,” he said.

Government sources told Fox News before the announcement that the speech would form the basis for new legislation he hopes to get before the Senate next week. The proposal is similar to a compromise put forward by Sen. Lindsey Graham, R-S.C., that would include three year work permits for DACA recipients and extension of legal status for TPS holders, in exchange for the wall funding. Graham called the proposal "fantastic" in a tweet after the announcement.

"Let's get it done," he tweeted. House Republicans were scheduled to be briefed about the proposal in a conference call at 5 p.m. ET.

Senate Majority Leader Mitch McConnell, R-Ky., praised Trump for his "bold solution" to re-open the government.

“Compromise in divided government means that everyone can’t get everything they want every time," McConnell said in a statement. "The President’s proposal reflects that. It strikes a fair compromise by incorporating priorities from both sides of the aisle."

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Likewise, Sen. Mitt Romney, R-Utah, voiced support for the president's compromise plan, pledging his support for it via Twitter.

"@POTUS has put forth a reasonable, good faith proposal that will reopen the government and help secure the border. I look forward to voting for it and will work to encourage my Republican and Democratic colleagues to do the same," Romney wrote.

But Trump’s proposal was quickly swatted down by Democrats. Indeed, House Speaker Nancy Pelosi came out ahead of the announcement to say the anticipated proposal comprised a "compilation of several previously rejected initiatives, each of which is unacceptable and in total, do not represent a good-faith effort to restore certainty to people’s lives."

"It is unlikely that any one of these provisions alone would pass the House, and taken together, they are a non-starter," she said in a statement. "For one thing, this proposal does not include the permanent solution for the Dreamers and TPS recipients that our country needs and supports." 

Striking a similar tone, Senate Minority Leader Chuck Schumer, D-N.Y., said it was unfortunate that in an effort to resolve the shutdown, Trump "keeps putting forward one-sided and ineffective remedies."

He urged the president to open up the government as a prelude to productive and bipartisan solutions on immigration and the southern border.

"It was the president who singlehandedly took away DACA and TOS protections in the first place," Schumer's statement read. "Offering some protections back in exchange for the wall is not a compromise, but more hostage taking."

The partial government shutdown, which has dragged on for 29 days and led to hundreds of thousands of federal workers being furloughed or working without pay, is the result of Republicans and Democrats being unable to come to an agreement over Trump’s demand for wall funding. Trump has said he will not sign a bill to open the government unless it includes that funding, while Democrats have refused to consider the $5.7 billion figure, instead offering $1.3 billion for general border security.

Trump’s move marks a rare outreach in a week where both sides appear to have hardened in their positions, with Trump canceling a Democratic delegation’s military flight to Afghanistan after House Speaker Nancy Pelosi called on him to delay his State of the Union address earlier in the week. On Saturday before the speech, Trump described Pelosi as being “controlled by the radical left.”

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Senate Democratic Whip Dick Durbin, D-Ill., also rejected the proposal ahead of the announcement.

“First, President Trump and Senate Majority Leader [Mitch] McConnell must open the government today. Second, I cannot support the proposed offer as reported and do not believe it can pass the Senate. Third, I am ready to sit down at any time after the government is opened and work to resolve all outstanding issues,” he said in a statement.

Pelosi said that Democrats intended to pass six bills next week and other legislation to open the government, "so that we can fully negotiate on border security proposals."

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“The president must sign these bills to re-open government immediately and stop holding the American people hostage with this senseless shutdown.  Each day he prolongs this needless crisis, Coast Guardsmen, FBI agents, border patrol officers, TSA agents, and hundreds of thousands more workers are forced to live without knowing how they can feed their families or pay their bills," she said in her statement.

Fox News’ John Roberts, Chad Pergram, Ben Florance and Jason Donner contributed to this report.