US President Donald Trump's mixed reception from football fans on his political home turf in the US south on Monday underscored the risk in his unrelenting and contentious focus on core supporters.

The 45th president rarely moves outside his comfort zone, and so it was meant to be on a two-state whirlwind tour Monday.

Trump visited the conservative bastions of Tennessee and Georgia, cozying up to farmers and throwing red meat to college football fans by attending a championship final game.

The day -- flush with paeans to gun ownership, the flag and life at home on the ranch -- was a decent snapshot of Trump's first 12 months in office.

Since entering the White House, Trump has played squarely to his conservative base, with uncompromising positions on immigration and a host of wedge issues.

"Oh are you happy you voted for me?" he told members of the Farm Bureau, a farmers group, who applauded wildly. "You are so lucky that I gave you that privilege."

White House aides assume he is already running for reelection in 2020, and they are betting his coalition of rural, white and conservative voters can deliver another victory.

But that looks like an increasingly risky proposition.

Like predecessor Lyndon Johnson, Trump's movements have been limited by his deep unpopularity.

His approval ratings nationwide are around 35-40 percent and in some states they are even more anemic.

Whole swathes of the country are virtual no-go zones.

He is the first president in decades not to visit the country's most populous and economically important state, California, in his first year in office.

On Monday, in Atlanta, as he strode to midfield to observe the nation anthem in a college football championship, a chorus of boos blended between the cheers to serve as a small but symbolic warning.

While Trump's most vociferous supporters, including his son Donald junior played down the jeers -- and in some case even denied they happened -- some in the Republican party will worry.

A Republican president, visiting the south, during a sports event between two overwhelmingly right-leaning states should be an easy victory.

Already, party stalwarts are concerned about what is in store for November congressional elections.

"If Trump's approval rating is still in the thirties on election day, it's going to be an extraordinarily tough environment for Republicans," said Alex Conant, a Republican operative with Firehouse Strategies.

- 'Tough to do' -

"Just as important as raising his favorable ratings is lowering his strong disapproval ratings. That will be tough to do if he's only focused on his base."

Yet Trump has shown a marked unwillingness to modulate his attack-dog approach.

In speech after speech, he lampoons the media, courts right-wing adulation and attacking immigrants and his many critics.

On Monday his administration gave an estimated 200,000 Salvadorans 18 months to leave the country.

But buried in Monday's speech there was perhaps the very faintest glimmer of a broadening of his strategy -- with Trump making a play for African American votes by underscoring falling unemployment rates in that community.

And on landing in Georgia he also signed into law measures creating a national historic park for Martin Luther King Junior, and was joined by on Air Force One by Alveda King, the slain pastor's niece.

He notably did not tweet about Oprah Winfrey, amid fevered -- and largely unsubstantiated -- speculation that she may challenge him in 2020.

Still, courting African-America voters will be a difficult gambit for a politician who cut his teeth by criticizing America's first black president.

And there are already signs that Republicans are preparing the ground for a less than stellar showing in November.

"Historically," Vice President Mike Pence told US radio channel "you have to acknowledge that the first midterm election for the party in power in the White House is always challenging."

It could be especially challenging for such a polarizing president.