WASHINGTON -- After six months of infighting, investigations and legislative failures, U.S. President Donald Trump is trying to combat new signs of weakness in his Republican base and re-energize his staunchest supporters.

White House officials have been urging the president to refocus on immigration and other issues that resonate with the conservatives, evangelicals and working-class whites who propelled him to the Oval Office. The president has ramped up his media-bashing via Tweet, long a successful tactic for Trump, and staged rallies hoping to marshal his base to his defence.

The effort underscores Trump's shaky political positioning not yet seven months into his presidency. Trump has remained deeply unpopular among Democrats, and there are signs that his support among Republicans may be softening. His advisers are aware that a serious slip in support among his core voters could jeopardize hopes for a major, early legislative accomplishment and would certainly increase Republicans' worries about his re-election prospects.

White House counsellor Kellyanne Conway acknowledged the concerns Sunday on ABC, saying the president's approval rating "among Republicans and conservatives and Trump voters is down slightly."

"It needs to go up," she said.

In a Monday morning tweet, Trump dismissed his adviser's statement. "The Trump base is far bigger & stronger than ever before," he wrote on Twitter. He later insisted that his support "will never change!"

But polling doesn't support Trump's claim. A recent Quinnipiac University survey showed the president's approval dipping into negative territory among whites without college degrees -- a key group of supporters for the president. The percentage of Republicans who strongly approve of his performance also fell, with just over half of Republicans saying they strongly approved of Trump. That's down from the two-thirds of Republicans who strongly approved of the president's performance in June.

Just one-third of all Americans approved of his job performance, a new low in the poll.

The president's struggles already have prompted public speculation about his political future. The White House pushed back angrily Sunday against a New York Times report about Republicans preparing for 2020 presidential race that may not include Trump. The report described Vice-President Mike Pence as laying groundwork in case Trump does not run. Pence called the report "disgraceful."

The chatter has been fueled by Trump's unsuccessful attempt to shepherd health care legislation through Congress, the drip-drip of revelations about his associates' ties to Russia and the churn of turnover and turmoil at the White House. The president's advisers have tried to drown out the bad news by focusing on his agenda.

"They are telling him just enact your program," Conway said of the president's base. "Don't worry about a Congress that isn't supporting legislation to get big ticket items done. And don't worry about all the distractions and diversions and discouragement that others, who are trying to throw logs in your path, are throwing your way."

In a televised event at the White House last week, the president endorsed legislation that would dramatically reduce legal immigration to the United States. The bill is unlikely to ever become law, but that mattered little to Trump's advisers. Their barometer for success was the reaction from conservatives like commentator Ann Coulter, who called the White House's embrace of the controversial legislation "the best moment of the Trump presidency since the inauguration."

Immigration is expected to continue being a focus for Trump in the coming weeks, including a push for the border wall. Officials also are weighing a more public role for White House policy adviser Stephen Miller, a favourite of Trump backers whose hard-line immigration policies irritate some congressional Republicans.

The appointment of White House chief of staff John Kelly also fits in to that effort. While Kelly was brought in primarily to bring much-needed discipline to the West Wing, officials note that he, too, is viewed favourably by some Trump loyalists for his early execution of the administration's immigration policy as secretary of the Department of Homeland Security. Kelly's appointment was particularly welcomed by senior strategist Steve Bannon, who has taken on the task of ensuring Trump doesn't drift from the promises he made to his base during the campaign.

Several White House officials and Trump advisers insisted on anonymity in order to discuss the ways the administration is moving to shore up support for the president.

Like Trump's embrace of the legislation curtailing legal immigration, some of what the president has to offer his core supporters is more show than substance. In late July, Trump announced on Twitter that he was banning transgender people serving in the military -- a policy shift sought by social conservatives -- despite the fact that the Pentagon had no plans in place to enact the change. The policy is now being crafted.

Alice Stewart, a conservative who worked for the presidential campaigns of Sen. Ted Cruz, R-Texas, and former Arkansas Gov. Mike Huckabee, said Trump is right to make overtures toward his coalition of loyal supporters, even if some of his moves are incomplete.

"I think people realize half a loaf is better than none," Stewart said.

Mitch Harper, a former GOP state legislator and Republican activist in Indiana, said Trump will get credit from conservatives even for partial measures simply because he is "articulating things that they have not heard anyone articulate in a long time."

And what about the results? Harper said Trump supporters "are willing to wait."

Indeed, even some of Trump's advisers still marvel at the loyalty of the president's supporters. For now, conservatives are pinning the blame on Washington's failure to get health care done not on Trump, but on the handful of Republican senators who blocked legislation aimed at overhauling "Obamacare."

"I think on health care the president is viewed as someone who did everything they could," said Matt Schlapp, who heads the American Conservative Union.

Associated Press writers John Raby in Huntington, West Virginia, and Catherine Lucey in Bridgewater, New Jersey, contributed to this report.