Thousands of people were descending Saturday on Washington's National Mall and other cities across America in opposition to the policies of Donald Trump, in the largest protests since he returned to the White House.

At a time of spreading global resentment against the Republican president, rallies took place earlier in international capitals including Paris, Rome and London.

A loose US coalition of dozens of left-leaning groups like MoveOn and Women's March organized "Hands Off" events in more than 1,000 towns and cities and in every congressional district, the groups say. 

The unifying theme: the growing resentment of what the group Indivisible has called "the most brazen power grab in modern history," led by Trump, his advisor Elon Musk "and their billionaire cronies."

Trump has angered many Americans by moving aggressively to downsize the government, impose his conservative values and sharply pressure even friendly countries over trade terms — causing stock markets to tank.

"Trump, Musk, and their billionaire cronies are orchestrating an all-out assault on our government, our economy, and our basic rights — enabled by Congress every step of the way," Indivisible said on its website.

Many Democrats are irate that their party, in the minority in both the House of Representatives and Senate, has seemed so helpless to resist Trump's aggressive moves. 

The largest protest Saturday is expected to take place starting at noon (1600 GMT) just blocks from the White House, on the National Mall in Washington, with prominent Democrats including Representative Jamie Raskin set to address the crowd. 

Separately, a March for Palestine has been scheduled in Washington around the same time.

Saturday's demonstrations could offer a temperature reading of just how hot voters' feelings are.

A Women's March protest shortly after Trump's first election in 2016 drew an estimated half-million people to Washington; advance estimates for Saturday's turnout have been far smaller. 

As Trump continues aggressively shaking things up in Washington and beyond, his approval rating has fallen to its lowest since taking office, according to recent polling.

But despite pushback around the globe to his sweeping imposition of tariffs, and bubbling resentment from many Americans, the White House has dismissed the protests, and the Republican president has given no sign of relenting.

"My policies will never change," he said Friday.