(CNN) President Donald Trump is slamming the constitutionally protected provision of birthright citizenship as a "crazy, lunatic policy" in an incendiary endgame to the midterm election campaign, which could save the Senate but risks putting the House beyond reach.

With four days to go, Trump is riding the strategy on which he has effectively bet his presidency -- a refusal to broaden his coalition and incessant appeals to his base -- into its biggest test so far. Yet his approach risks alienating more moderate voters in tight House races.

In one example of his all-in play to his most loyal supporters, Trump issued a new attack on the 14th Amendment, which guarantees that even children born on US soil to undocumented immigrants are American citizens, at a rally Thursday night in Missouri. The President has dubiously argued he has the power to override the provision with an executive order.

And a day after unveiling the most racist national political ad in a generation, Trump vowed tough restrictions on asylum and turned his attention to consolidating GOP power in a trip to Missouri to support one of his proteges, Josh Hawley, who is well placed to unseat Democratic Sen. Claire McCaskill.

The President even said that the US troops he plans to dispatch to the border to address what he claims is a national crisis could turn their guns on members of a migrant group -- currently hundreds of miles away in Mexico -- if they threw rocks at the troops.

"Democrats want open borders and want to invite caravan after caravan into our country," Trump told the euphoric, fired-up crowd, which lapped up his fiery rhetoric on immigration and chanted "Build that wall! Build that wall!" in a display of the potency of the issue among the President's base.

The unusually distinct races for the two chambers of Congress this year mean that a scorched earth message that works well in Senate races in Trump country may backfire in House contests in more moderate territory.

But in the final days of the campaign, the President has escalated rhetorical assaults on undocumented immigrants and the traveling migrant group to new heights, delighting base voters but infuriating Republicans in swing districts and GOP strategists worried about the House.

That, and a travel schedule that appears to be mostly geared to getting red state Senate candidates over the line and toppling vulnerable Democrats, suggests the President can read the polls just as well as anyone else.

Most pundits are staying away from predictions after Trump's shock win over Hillary Clinton in 2016. But a majority of models suggest the most likely outcome on Tuesday is that Democrats take the House and Republicans keep control of the Senate or even increase their majority by a couple of seats.

CNN's Harry Enten assesses in his forecast that Democrats will win 225 seats -- and the House majority -- while Republicans will fall to 210 seats. A Democratic win of 202 seats or 262 seats is within the margin of error.

Republicans will hold 52 seats -- and keep the majority -- in the Senate, while Democrats will hold just 48, according to Enten's analysis. Anything between Republicans holding 48 seats and 56 seats is within the margin of error.

Using presidential symbolism to sell a campaign message

Trump has been flinging flaming campaign trail attacks on immigration for days.

But on Thursday he chose the ornate surroundings of the Roosevelt Room of the White House, often the venue for solemn state announcements, for what was billed as a major policy announcement on asylum.

Yet what followed was a meandering speech , packed with misrepresentations and falsehoods, that lacked the big new plan that White House officials had promised -- other than a vague undertaking to issue an executive order next week.

It was the latest indication that Trump's improvisational and politically motivated pronouncements often have his policy team struggling to catch up. The same thing happened when the President suddenly pledged last month to unveil a middle-class tax cut in the next few weeks -- even though Congress, which has the power of the purse -- was not in session at the time.

The White House has since signaled there will be no movement on tax cuts until January at the earliest.

In place of a major new policy proposal on asylum, the President cranked up the demagoguery, suggesting US troops could actually open fire on members of a migrant group if they ever reach the border.

"They want to throw rocks at our military, our military fights back," Trump said. "When they throw rocks like they did at the Mexico military and police, I say consider it a rifle," he said, setting out a scenario that is unlikely to come to pass and one of disproportionate force.

His warning alarmed former Republican Sen. Chuck Hagel, who served as secretary of defense in the Obama administration.

"My reaction ... is one of disgust. That is a wanton incitement of unnecessary violence. It is a distraction, It is a distortion, it is a rank political purpose to use our military like this," Hagel told CNN's Jake Tapper.

"Not in my lifetime have I ever heard those kind of words from a President of the United States."

JUST WATCHED Hagel: Trump is using our troops as pawns Replay More Videos ... MUST WATCH Hagel: Trump is using our troops as pawns 03:16

Trump also said the military was building tent cities for detained migrants, when military officials have said no such construction is underway. He also falsely claimed that his administration has started building his famed border wall, taking credit for an existing project by the federal government to replace one section of fence with a wall.

His latest escalation followed his tweet promoting a campaign video on Wednesday night that effectively equated the Central Americans in the traveling migrant group with a convicted murderer who killed two California deputies.

Hardcore message undercuts Republicans in tight House battles

The President's incessant, incendiary focus on immigration is frustrating some of his fellow Republicans, who have the fate of the House, especially, in mind.

Rep. Ryan Costello, a moderate from Pennsylvania who is retiring after the election, warned that Trump's message could be the last straw for endangered GOP House members.

"I think closing on doom and gloom and scaring people over immigration, that is not going to bring home undecided voters in swing districts," Costello told CNN's Lauren Fox.

"I can't imagine anybody in a close district wants the closing argument to be immigration," Costello said. "Your local message is in competition with what the President is talking about."

Other Trump supporters are frustrated that the President is not talking exclusively about the economy , which grew at 3.5% in the third quarter, has taken the unemployment rate to a 50-year low of 3.7% and has promoted soaring business and consumer confidence.

New jobless figures are expected to give Trump a further boost on Friday with the final release of data from the Bureau of Labor Statistics before the election.

But the President has clearly made a decision on the most profitable way to end his campaign -- and he has opted to be true to the populist, politically incorrect persona that won him the White House in the first place.

It's possible the House was already out of reach, given his approval rating in the mid-40s, the fact that many vulnerable GOP lawmakers are running in districts that Clinton won and historical portents that suggest first-term presidents always struggle in the midterm elections.

New polling from CNN suggests that in Trump country at least, his instincts for what his voters want are shrewd.

Among likely Republican Senate voters in Florida, immigration is now an important issue for 33% of voters, up from 22% in mid-October, before he hit on his flaming midterm election closing argument.