United States President Donald Trump got a rock star reception in the Lone Star state on Monday in one of the highlights of his rally blitz ahead of the Nov 6 mid-term elections.

Giant banners with a picture of him standing with folded arms and jutting jaw hung all around the ceiling of the cavernous 18,000-seat Toyota Centre in Houston, Texas.

The rally was essentially held to boost the fortunes of Senator Ted Cruz, who faces an uncommon challenge in a deeply Republican state from Democratic candidate and congressman Beto O'Rourke, who has come within a whisker of him in opinion polls.

Dr Ed Young, pastor of the Second Baptist Church of Houston, which boasts a following of some 70,000, opened the rally with a speech that cast the battle in religious overtones.

"Which way, America?" he intoned. "Will we continue to be a Republic under God or will we slouch towards godless socialism?"

To frenzied cheers, President Trump hit his usual talking points, highlights among them include the robust economy, low unemployment and tax cuts - of which he promised a further 10 per cent cut for the middle class.

He railed against Mr O'Rourke's plans for socialist healthcare and insisted that the Democrats wanted to abolish the Second Amendment - which guarantees the right to have guns - as well as Immigration and Customs Enforcement (ICE), the federal agency which, among other things, is in charge of border control.

"The Democrats want to replace freedom with socialism," he thundered. "Mr O'Rourke is a "radical, open-borders left-winger", he added, as the audience responded with loud boos.

He went a step further to spell out his anti-globalist stand. "A globalist is a person who wants the globe to do well, frankly not caring about the country so much. You know, we can't have that," he said, to more loud boos from the crowd.

"You know what I am, I'm a nationalist," he said. "Use that word," he urged, as the crowd erupted in chants of "USA! USA!"

He then brought up his strongest talking point of the evening, the few thousand-strong caravan of unarmed migrants, including women and children, heading up from central Mexico to the US border.

The caravan is an "assault on our country", he said. Right-wing commentators in the media have amplified this, with some calling the caravan - which is still days away from the border - an "invasion".

President Trump on Tuesday repeated that he was contemplating sending the military to protect the border.

This election, he rasped, would be about the caravan, Supreme Court Justice Brett Kavanaugh, law and order, tax cuts and common sense.

Justice Kavanaugh came under severe pressure during his confirmation hearings earlier this month, after a woman accused him of sexually assaulting her while drunk when they were both in high school.

The Republicans, however, rammed through his confirmation, determined to achieve their prized goal of tipping the nine-member court bench towards the conservative side.

Mr O'Rourke, 46, has become the darling of the Democrats, with his sterling challenge against the incumbent Senator Cruz, 47, seen as evidence of the "blue wave" they hope will grab them a majority in the House and possibly even the Senate.

The Democratic candidate raised more than US$38 million (S$52 million) in the third quarter, a stunning sum that eclipsed Mr Cruz's US$12 million in the same period.

Still, Mr Cruz looks likely to fend off Mr O'Rourke, said analysts.

This is partly because Mr Cruz will get the loyal Latino vote. Also, while flipping Texas from Republican red to Democratic blue has been a longstanding dream of the Democrats, the state - outside of cities such as Houston and Austin - is staunchly Republican.

"I will be surprised if the Cruz versus O'Rourke race is close, and even more surprised if O'Rourke wins," Dr H.W. Brands, a professor of history at the University of Austin, told The Straits Times.

"Texas remains very Republican and though Cruz isn't popular, he's red," he said.

"But stranger things have happened," he cautioned. "Donald Trump won in 2016. So we'll just have to see how the votes fall."

Outside the Toyota Centre, a few thousand people watched the President on a big screen, cheering, clapping and booing on his cues. About halfway through his speech, some of them began to disperse as a cold drizzle started to fall. But the few hundred who stayed left no doubt about the appeal of the strongman.

"I work in law enforcement and our morale is much higher. We can do our jobs a lot easier now," said a 60-year-old who asked to be identified only by his first name, Charles.

"There's been a lot of good things," he said.

Justice Kavanaugh's appointment to the Supreme Court was a good thing and so was Mr Trump's support for the military and veterans, he added.

He and his friend, a retired undercover policeman, were full of praise for the President's tough stand on the border, including the controversial decision to build a wall.

"He actually does something. He doesn't sit on his butt and don't do nothing," Charles said. "He's done more in two years than five or six presidents put together. And the news media, I call it the communist news media, doesn't report it."

Mr Eric Maxwell, a 58-year-old African American who has his own energy consulting business, said: "I look on the Republicans as kind of protectors of capitalist society. I (shudder) to think what socialism will bring."

Mr Dave McBride, 37, a teacher, could not say if Mr Trump's policies have directly benefited him. But he credited the President for the power of positive thinking. "If you say America is great, who's to argue with that?" he said.

Mr John Pitt, a 45-year-old quality control manager for heavy construction in the US Army's Corps of Engineers, was forceful. "You know why I like President Trump? Because he will look at the people who need to be told this and he will tell them... F*** you. Straight up."