President Joe Biden laid flowers and prayed Tuesday at the site of America's latest deadly mass shooting, warning that the white supremacist ideology motivating the alleged gunman is tearing the country's "soul" apart.

In the hastily organized trip to Buffalo, New York, Biden, accompanied by his wife Jill Biden, reprised the wearily familiar role for presidents of consoler-in-chief.

The first couple began by laying a bouquet at a makeshift memorial outside the neighborhood supermarket where a white gunman allegedly murdered 10 African Americans on Saturday.

A strong breeze tugged at balloons and flowers piled under a tree while the Bidens paid their respects, the president making the sign of the cross before giving way to a delegation of elected officials laying their own bouquets.

Biden then went into private meetings with relatives of the victims and first responders, where the White House said he was offering "condolences and comfort to those affected by this tragedy."

Biden was later scheduled to deliver a speech that, like so many he has given, will urge Congress to overcome division on restricting firearms ownership, a constitutionally protected right that has led to there being more guns than people in the world's richest nation.

After decades of mass shootings in schools, nightclubs, movie theaters and churches, many Americans are numb to each new outrage, while presidents have repeatedly discovered their powerlessness to change laws in the face of a reluctant Congress.

In Saturday's rampage, the killer wielded an AR-15, a military style weapon which has been used repeatedly in mass shootings around the country while at the same time being one of the most popular rifles for legitimate gun enthusiasts.

Having long campaigned unsuccessfully to ban assault-style rifles, Biden will once more demand laws to "keep weapons of war off our streets," the White House official said.

He will also highlight the failure to keep firearms away from people with serious mental illness who are "a danger to themselves or others."

Racist ideology

The most acute portion of Biden's remarks could be about a deeper rooted threat to the nation -- the racism and extremism that the 79-year-old Democrat cited as motivations for first coming out of retirement to take on then president Donald Trump in the 2020 election.

In a preview of the speech, the White House official signaled strong wording from Biden, who will "call this despicable act for what it is: terrorism motivated by a hateful and perverse ideology that tears at the soul of our nation."

"He'll call on all Americans to give hate no safe harbor, and to reject the lies of racial animus that radicalize, divide us, and led to the act of racist violence we saw on Saturday," the official said.

Biden also will call on Americans "to seek a more perfect union that embraces the diversity that has made us the strongest and most dynamic nation in the history of the world."

The suspect captured after the shooting was said by police to have authored a lengthy manifesto promoting extreme, but increasingly widely held, white supremacist ideas.

At the heart of the manifesto was a rant about what's dubbed "replacement theory," which purports the existence of a leftist plot to dilute the white population with non-white immigrants.

It is a conspiracy theory that, like the bizarre QAnon narrative, has spread from the furthest fringes of society to surprisingly mainstream areas -- most notably Tucker Carlson's enormously influential nightly talk show on Fox News.

Prominent Republican members of Congress have also echoed "replacement theory" talking points, which in turn are not too distant from Trump's multiple speeches as president in which he demonized illegal immigrants as invaders, once calling them "animals."