When it came to immigration, President Donald Trump’s speech to Congress on Tuesday night was more notable for what it left out than for what it included.

Just hours earlier, Trump had told reporters he would consider legalizing some undocumented immigrants — a massive shift in policy — as part of a bipartisan deal. But his address had no mention of the idea and instead included familiar passages denouncing crime by undocumented immigrants and celebrating recent moves to boost deportations.

“By finally enforcing our immigration laws, we will raise wages, help the unemployed, save billions of dollars, and make our communities safer for everyone,” Trump said in his remarks.

While Democrats brought DREAMers as guests, Trump invited families whose loved ones had been murdered by undocumented immigrants and he described their suffering. The president touted a new government office, Victims Of Immigration Crime Engagement (VOICE), that would focus on their plight.

Trump did say that “real and positive immigration reform is possible,” but only mentioned conditioning legal immigration on job skills rather than family ties. It’s a popular idea, a version of which was included as part of the 2013 “Gang of Eight” bill that passed the Senate and died in the House.

Related: Trump Honors Tearful Wife of Navy Seal

The president surprised many earlier in the day when he told reporters in a pre-speech meeting that he was open to providing legal status to undocumented immigrants who haven't committed serious crimes. Those individuals would not need to leave the country first.

“The time is right for an immigration bill if both sides are willing to compromise,” Trump told reporters.

It was an out-of-left-field move, but White House sources indicated to NBC News that the remarks were not the kind of idle comments by Trump that have roiled news cycles in the past.

One administration official described it as an effort by Chief of Staff Reince Priebus and Trump’s son-in-law Jared Kushner to find common ground and said that even top adviser Stephen Bannon, known for his anti-immigration views, had signed off.

Activists and lawmakers on both sides of the issue seemed unsure whether to take Trump seriously.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

“It’s our view Trump is engaged in a PR campaign to try to make himself sound like a reasonable guy on immigration, but what they’re doing in practice and what they’re putting in place on policy is the most radical nativist agenda we've seen in modern America,” said Frank Sharry, executive director of immigration advocacy group America’s Voice.

After Trump’s speech hit his usual notes on immigration, Sharry derided the president's earlier talk of compromise as “a cruel hoax.”

Advocates who favor restricting immigration took a cautious approach.

“We continue to oppose amnesty, but we'll wait and say what the administration proposes here,” Ira Mehlman, media director at the restrictionist Federation for American Immigration Reform, told NBC News.

Senate Minority Leader Chuck Schumer batted away a reporter’s question on bipartisan reform, instead blasting Trump’s “incompetence” on immigration and calling on him to undo his recent executive orders on the issue.

Senator Marco Rubio, who was in the “Gang of Eight,” cautioned that “it will take a lot of work” to reach a deal but told NBC News he could potentially get involved again.

Others encouraged Trump to take the plunge.

“We’ve been ready,” Rep. Michelle Lujan Grisham (D-NM), chair of the Congressional Hispanic Caucus, said in a statement. Rep. Mario Diaz-Balart (R-FL), a leading advocate for immigration reform in the House GOP, said he was “very encouraged” by Trump’s comments.

There were many reasons to be skeptical, however, of both of Trump’s intentions and his ability to get a bill passed.

For one, Trump has hinted at shifts in immigration before only to quickly recommit to a hardline approach. Some of his most trusted advisers, including Bannon, Stephen Miller and Attorney General Jeff Sessions, were major players in past efforts to torpedo immigration reform. It would be astounding if Trump broke with them on such a fundamental issue.

Actions also speak louder than words. The administration is in the midst of a major crackdown on illegal immigration that empowers authorities to target undocumented immigrants who have not committed major felonies, a reversal of Obama-era orders.

It’s possible Trump has been moved by stories of arrests and deportations under his watch, like a mother of two American children or a popular restaurant manager in a pro-Trump coal town in Illinois. But it would be an odd move to tout the benefits of increased removals and then cut a deal to allow the same people to stay.

Related: Fact-Checking Trump's first address to Congress

Then there’s the question of how and when to negotiate a bill. Republican leaders in Congress are already bogged down in debates over legislation on health care and taxes, their two top priorities for the year. They have yet to move on infrastructure, another issue where Trump called for major action on Tuesday night. It would be a major stretch to add comprehensive immigration reform to the mix, a politically charged issue that divides the GOP far more than the other items on Trump's agenda.

It’s still not clear what an immigration deal would look like based on Trump’s limited comments.

The president has indicated repeatedly that he does not want to deport DREAMers, the young undocumented immigrants who were protected under a program created by President Barack Obama. It’s possible he could float a limited compromise trading more enforcement for legal status, but Democrats and activists would be unlikely to back a plan that cemented their status while also ramping up efforts to deport their parents and older siblings.

As for a broader deal, though, it might work. The “Gang of Eight” bill included new enforcement measures favored by Trump, included an expanded border patrol and new rules requiring employers to check new hires against a database, known as E-Verify, to see whether they eligible to work. It even included requirements to complete more fencing along the border. It’s possible Democrats could accept even further measures in exchange for a path to legalization.

But the substance of the immigration debate has become more complex since the “Gang of Eight” bill. That could make things more difficult, even with Trump’s credibility with his base there to reassure Republicans nervous about being tagged as soft on “amnesty.”

The biggest shift is on legal immigration. There was a relatively broad consensus at the time that reform should encourage more immigration to grow the economy and expand the use of work visas. That consensus has unraveled since then with some Republican senators urging dramatic reductions in immigration.

Sessions and Bannon have long criticized legal immigrants and temporary workers as a drain on American wages. If they demanded a decrease in immigration as part of a deal, it could be difficult to get Republicans and Democrats on board even if they could agree to concessions elsewhere.

Finally, the politics have also changed on the Democratic side. In 2013, Republicans were reluctant to vote for any bill that looked like a win for Obama and might expose them to a backlash from the talk radio right. Now, Democrats are the ones under pressure from their own base to refrain from negotiating with Trump.

“Even if the leadership took it up, the rank and file would revolt, and how could Democrats suddenly become Trump partisans?” asked Mark Kriorian, executive director of the Center for Immigration Studies, which favors lower immigration levels. “It would actually be kind of hilarious, if it weren't for the fact that it would basically be the end of his administration.”

If nothing else, though, Trump is unpredictable. Plenty of presidents before him have been tempted by the promise of big ticket bipartisan reforms when their main agenda becomes stifled. It’s worth keeping an eye on whether Trump offers a more substantive olive branch in the future.