U.S. President Donald Trump condemned protests in Portland, Oregon, and violence in "Democrat-run" cities on Sunday as his Republican administration prepared to intervene in urban centers he says have lost control of anti-racism demonstrations.

Federal law enforcement officers, armed with a new executive order aimed at protecting U.S. monuments, last week started cracking down on crowds gathering in Portland to protest police brutality and systemic racism.

Facing declining polling numbers before his November 3 election against Democrat Joe Biden, Trump is making "law and order" a central campaign issue to appeal to critical suburban voters.

The crackdown in the liberal bastion of Portland drew widespread criticism and legal challenges as videos surfaced of camouflage-clad officers without clear identification badges using force and unmarked vehicles to arrest protesters without explanation.

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Unmarked cars and Federal Police: Protesters in Portland faceoff against authorities

Oregon's governor and Portland's mayor, both Democrats, called the move an abuse of power by the federal government and the state filed a lawsuit against the U.S. agencies involved.

Trump did not back down on Sunday.

"We are trying to help Portland, not hurt it. Their leadership has, for months, lost control of the anarchists and agitators. They are missing in action. We must protect Federal property, AND OUR PEOPLE," Trump wrote in a Twitter post.

Nationwide crackdown

White House Chief of Staff Mark Meadows said Attorney General William Barr and Acting Homeland Security Secretary Chad Wolf are working on measures the administration can take to counter the unrest.

"You'll see something rolled out this week as we start to go in and make sure that the communities, whether it's Chicago or Portland, or Milwaukee, or someplace across the heartland of the country, we need to make sure our communities are safe," Meadows said on "Sunday Morning Futures."

The announcement is expected to expand a new Justice Department initiative that sends federal law enforcement into cities facing protests.

Portland Mayor Ted Wheeler said on Sunday the federal authorities were sharply escalating the situation.

"Their presence here is actually leading to more violence and more vandalism," Wheeler said on CNN's "State of the Union" program. "And it's not helping the situation at all. They're not wanted here. We haven't asked them here. In fact, we want them to leave."

In an interview on "Fox News Sunday," Trump attributed the increase in violence in cities such as Chicago and New York by saying "they're Democrat-run cities, they are liberally run. They are stupidly run."

The Republican president last month threatened to send U.S. military to quell protests that erupted over police brutality and racism after the killing of unarmed African American George Floyd by a Minneapolis police officer.

Oregon's attorney general, Ellen Rosenblum, on Friday filed a federal lawsuit against the Department of Homeland Security (DHS), the U.S. Marshals Service, and Customs and Border Protection (CBP), saying they had violated peoples' civil rights by seizing and detaining them without probable cause.

The American Civil Liberties Union is calling the situation in Portland a "constitutional crisis." It filed a lawsuit on Friday against DHS and the U.S. Marshals Service and promised more suits in the coming days.

A CBP spokeswoman said last week that agents had been deployed to Portland to support a newly launched DHS unit charged with enforcing last month's executive order here from Trump to protect federal monuments and buildings.

House Democrats demand investigation

Democrats in the U.S. House of Representatives asked the internal watchdogs for the Justice and Homeland Security departments to launch an investigation into whether they have "abused emergency authorities" in order to justify targeting peaceful protesters last week in Portland.

In a joint letter to the inspectors general for the two departments, lawmakers said they were concerned that Barr and Wolf were using federal agents to "suppress First Amendment protected activities in Washington, D.C., Portland and other communities."

Inspectors general sit inside executive branch agencies, having a unique duty to report their findings to both Congress and agency heads.

Representatives for Justice and Homeland Security and their inspector general offices did not immediately respond to requests for comment on the Democrats' letter.

The letter was signed by House Judiciary Committee Chairman Jerrold Nadler, House Homeland Security Chairman Bennie Thompson and House Oversight Committee Chairwoman Carolyn Maloney.

"This is a matter of utmost urgency," they wrote. "Citizens are concerned that the administration has deployed a secret police force, not to investigate crimes, but to intimidate individuals it views as political adversaries." 

(With input from Reuters)