BED MINSTER, United States — Beset by investigations, dire approval ratings and growing party dissent, Donald Trump is stirring up his base, hoping to mobilize an army of political shock troops to protect his presidency.

Revelations that a grand jury has been impaneled to investigate his finances and his campaign's ties to Russia raises the specter of indictments and subpoenas that would shake any administration.

But for Trump, who is just six months into his presidency, it represents more turmoil after an exodus of top White House officials and humiliating recent reverses in Congress.

Despite a healthy economy, a new poll by the Connecticut-based Quinnipiac University shows his approval rating at 33 percent — the same level endured by Richard Nixon during the Watergate scandal or George W. Bush after the grind of the Iraq war.

Facing the prospect of limping through another three and a half years, Trump is settling on a strategy of shoring up the support of voters who propelled him to the White House with a series of right-wing policy announcements and red-blooded speeches.

In little more than a week, Trump has encouraged police to dole out rough justice, summarily threatened to kick transgender personnel out of the military and played up the threat of Hispanic gangs.

After warning that neighborhoods are "becoming blood-stained killing fields" he appeared in the Roosevelt Room of the White House last week to champion a massive curb on legal immigration.

The next day, Trump addressed thousands of supporters at a rally where many of the themes that served him so well in the presidential campaign were dusted off again — including blistering attacks on his defeated rival Hillary Clinton.

Hitting his notes on immigration and law and order, Trump painted the grand jury investigation into his campaign's ties with Russia as a personal threat to him and his supporters.

"The Russia story is total fabrication," he said, a "fake story that is demeaning to all of us and most of all demeaning to our country and demeaning to our Constitution."

Given that the thrice-wed New Yorker married an immigrant and many critics have said his recent announcements smack of hypocrisy.

There is still little clarity on how the ban on transgenders can be implemented while White House sources admit that the immigration proposal has scant hope of passing through Congress.

Emily Ekins, polling director at the CATO Institute, believes it is too simplistic to think of Trump voters as a homogenous group, but rather a loose coalition of conservatives, free marketers, cultural preservationists, anti-elites and the politically disengaged.

But, she says, opposition to immigration is a rare common thread running through most of the US president's base.

"The thing that really made this election distinctive were attitudes toward immigration, his core supporters were the most energized on the issue of immigration," Ekins told AFP.

"People ask 'is there anything he could have done to get his core supporters to abandon him?' There is one thing. If he were to back-track on immigration I think that would have been the thing to invalidate him in their eyes."

After losing a key vote on health care and then having his hands tied on dealing with Russia by a vote on sanctions that he has tried to disown, Trump has become openly critical of Congress — even though his Republican party has a majority in both houses.