American schoolchildren will be taught greater respect for patriotic values, Donald Trump promised on Thursday, as he followed up his surprise trip to Mexico and key anti-immigration speech by stepping up his appeal to “Americanism”.

The Republican presidential candidate defied expectations that he would soften his stance on the issue on Wednesday night, when he returned to the US from a suprisingly conciliatory joint press conference with the Mexican president only to give a fiery speech vowing to deport millions of undocumented immigrants to a crowd in Arizona.

On Thursday morning he kept up this populist tone, telling an enthusiastic audience at the American Legion convention in Cincinnati: “We will stop apologising for America, and we will start celebrating America.”

A Trump administration, he said, would consult with the military veterans’ group to promote “pride and patriotism” in schools – “teaching respect” for the US flag and pledge of allegiance.

“That flag deserves respect, and I will work with American Legion to help to strengthen respect for our flag,” said Trump. “You see what’s happening. It’s very, very sad. And, by the way, we want young Americans to recite the pledge of allegiance.

“One country, under one constitution, saluting one American flag … always saluting,” he added. “In a Trump administration, I plan to work directly with the American Legion to uphold our common values and to help ensure they are taught to America’s children. We want our kids to learn the incredible achievements of America’s history, its institutions and its heroes.”

One country, under one constitution, saluting one American flag … always saluting Donald Trump

The call to “advance the cause of Americanism – not globalism” came as Trump reiterated the anti-immigration message at the heart of his campaign, which delighted core supporters and dismayed his few remaining Latino allies, who had expected a tack towards moderation.

Despite a whirlwind visit to Mexico on Wednesday and suggestions of a softening in his approach to the issue, the campaign increasingly seems to be emphasizing nationalism as a tactic to defeat Hillary Clinton in November.

“We will be united by our common culture, values and principles – becoming one American nation,” said Trump in Cincinnati, where he spent half an hour touring the convention floor before heading to another nearby rally in the key swing state of Ohio.

Trump vowed anew to deport millions of undocumented people and to build a wall on the border with Mexico.

Speaking hours after a lightning visit to Mexico, Trump told a rally in Phoenix, Arizona, he was sticking with his plan for a “deportation force” to intercept those crossing the border illegally and hunt down criminal “illegal aliens” already in the US.

“We are going to take our country back,” he said, repeating a mantra from the primary campaign.

Speaking largely from a teleprompter, he also repeated his vow to make Mexico pay for a 2,000-mile wall which, he said, would bristle with sensors, towers and guards. “We will build a great wall along the southern border – and Mexico will pay for the wall, 100%. They don’t know it yet, but they’re going to pay for it.”

Trailing Clinton in the polls with just 69 days to the election, Trump and campaign aides had recently fuelled expectations of a “softening” of immigration policy, prompting speculation about a flip-flop.

Instead the speech, which his campaign billed as a major policy address, represented an abrupt reversion to an aggressive tone just hours after an unfamiliar conciliatory timbre in Mexico City, where Trump met President Enrique Peña Nieto.

The GOP nominee roused the crowd in Phoenix with grisly details about murders committed by undocumented immigrants. He brought on stage “angel moms” whose children were killed.

He spoke of cancelling an Obama administration programme that gives work permits to about 800,000 young immigrants who came to the US as children – a stance likely to slam shut any chance of Latino outreach.

Anybody who entered the US illegally would be subject to deportation and undocumented immigrants who committed any crime, not just felonies, would be detained and deported, he said. “There will be no amnesty.”

Trump also promised ideological tests for would-be visa applicants, a “sunset” on visa laws requiring Congress to rewrite them every few years and a ban on taxpayer funding for cities that don’t deport undocumented immigrants.

Asked by conservative radio host Laura Ingraham on Thursday morning whether this represented a “softening”, Trump replied: “Oh, there’s softening. Look, we do it in a very humane way … Obviously I want to get the gang members out, the drug peddlers out, I want to get the drug dealers out ... And then we’re going to make a decision at a later date once everything is stabilised. I think you’re going to see there’s really quiet a bit of softening.”

He added: “I feel strongly that we have to stabilise the border … We have to have a strong border, otherwise we don’t have a country.”

Wednesday’s rhetoric trampled over the hopes of Trump’s dwindling band of conservative Latino supporters. “This is how I feel: disappointed and misled,” tweeted Alfonso Aguilar, head of Latino Partnership for Conservative Principles. Jacob Monty, a member of Trump’s national Hispanic advisory council, resigned, Politico reported.

The rightwing columnist Ann Coulter, in contrast, exulted. “Wow. This doesn’t sound like ‘softening’. GO, TRUMP!!!” she tweeted.

Trump did, however, imply most of the estimated 11 million undocumented immigrants would remain untouched while his putative administration focused on deporting two million with alleged criminal records. “We will begin moving them out, day one. My first hour in office, those people are gone.”

On Thursday, at a lunchtime rally in Wilmington, Ohio, Trump was greeted by chants of “U-S-A, U-S-A, U-S-A” as he took his nationalist message back to the Rust Belt.

The state has been hit hard by a decline in manufacturing jobs and the campaign is seeking to weave together economic uncertainty with the uncompromising message on immigration.

“We will treat everyone with compassion but our greatest compassion will be for the American citizen,” Trump told an almost entirely white audience.

“No state has suffered more from bad trade deals,” he claimed. “Ohio has lost nearly one in three of its manufacturing jobs since Nafta and one in four since China entered the WTO [World Trade Organisation].”

National polls have begun to narrow again in recent days and although Clinton is still ahead in Ohio on average, the latest survey shows the candidates tied.

“A new era of American greatness is going to begin a little earlier than scheduled on 8 November,” Trump boasted, to wild cheers. “I think we’re going to win Ohio, big league.”