Russian meddling, national mourning for school shooting victims, the chaotic state of Donald Trump's presidency: US political turbulence forms a dramatic backdrop as conservatives gather near Washington beginning Wednesday for their often controversial annual confab.

Thousands of Republican activists, party heavyweights and national politicians -- not to mention a scion of France's ultra-nationalist movement -- converge on a Maryland convention center to tout the health of a populist revolution that rocked American politics to its core in 2016 and ushered in the Trump era.

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Thirteen months after the brash billionaire entered the White House, Trump is the featured speaker Friday at the Conservative Political Action Conference.

Religious conservative Vice President Mike Pence addresses CPAC the day before, as does White House counsel Don McGahn -- an odd choice for the high-profile event as he is under scrutiny in a White House security clearance scandal.

CPAC was "getting ready for another exciting event. Big difference from those days when President Obama held the White House," Trump tweeted Tuesday.

The newly inaugurated president received a hero's welcome when he addressed the conference last February.

A year earlier Trump was considered too controversial to attend. But such has been the rightward shift within the conservative movement that CPAC's organizers have invited French anti-immigrant champion Marion Marechal-Le Pen, a hardliner tipped as possible future leader of France's anti-immigrant National Front (FN), to speak shortly after Pence.

The 27-year-old former member of parliament, whose aunt, FN leader Marine Le Pen, was nearly endorsed by Trump last year in France's presidential race, is to mark her return to the public eye nine months after she said she was withdrawing from politics.

The move triggered a firestorm on Twitter, with mainstream Republican group The Reagan Battalion blasting CPAC for inviting "(Russian President Vladimir) Putin apologist and NATO hater" Le Pen.

Testy political climate

The conference comes at a time of heightened sensitivities on multiple fronts, including accusations that Trump's 2016 presidential campaign was illegally coordinating with Moscow.

Last Friday US special prosecutor Robert Mueller unveiled bombshell indictments against 13 Russians for allegedly running a secret campaign to tilt the 2016 US election in Trump's favor.

Trump repeatedly denies any collusion with Russia. But four Trump campaign officials have been indicted as part of Mueller's broader investigation, and attendees and speakers at CPAC will be watched closely on the issue.

They will also be faced with the scourge of US gun violence, after the latest in a string of deadly school shootings prompted national soul searching.

Trump strongly backs the constitutional right to bear arms. But he recently expressed support for legislation that would expand background checks for gun purchases, and ban devices which can turn legal semi-automatic weapons into machine guns.

Gun rights are front and center at CPAC -- two panels will address the issue on Saturday.

But while the National Rifle Association usually addresses CPAC, the country's largest pro-gun lobby is toning down its presence this year following last week's Florida massacre.

NRA Executive Vice President Wayne LaPierre was not listed on CPAC's schedule, but the gun group assured that he would address the conference.

Several Trump cabinet members, Republican lawmakers and combative former Milwaukee sheriff David Clarke are scheduled to speak.

Absent from the list: Mitt Romney, the 2012 Republican presidential nominee and recently announced US Senate candidate from Utah.

CPAC organizer Matt Schlapp declared him not conservative enough to attend.

The event will also be without rightwing provocateur Steve Bannon, the strategist who harnessed the populist insurgency that propelled Trump to victory, but was ousted from the White House last year.