Protesters have registered their rage against the new president in a chaotic confrontation with police who used pepper spray and stun grenades in a melee just blocks from Donald Trump's inaugural parade route.
Scores have been arrested for trashing property and attacking officers.
Several spirited demonstrations unfolded peacefully at various security checkpoints near the Capitol as police helped ticket-holders get through to the inaugural ceremony.
Signs read: "Resist Trump Climate Justice Now", "Let Freedom Ring", and "Free Palestine".
But about a mile from the National Mall, police gave chase to a group of about 100 protesters who smashed the windows of downtown businesses including a Starbucks, a Bank of America and a McDonald's as they denounced capitalism and Trump.
Police in riot gear used pepper spray from large canisters and eventually cordoned off protesters at 12th and L streets in northwest Washington.
The confrontation began an hour before Mr Trump took the oath of office and escalated several hours later as the crowd of protesters swelled to more than 1000, some wearing gas masks and with arms chained together inside PVC pipe.
One said the demonstrators were "bringing in the cavalry."
When some crossed police lines, taunting, "Put the pigs in the ground," police charged with batons and pepper spray, as well as stun grenades, which are used to shock and disperse crowds. Loud booms echoed through the streets about six blocks from where Trump would soon hold his inaugural parade.
Some protesters picked up bricks and concrete from the footpath and hurled them at police lines. Some rolled large, metal rubbish cans at police.
Police said in a statement that the group damaged vehicles, destroyed property and set small fires while armed with crowbars and hammers.
Peter Newsham, the interim police chief of the Metropolitan Police Department, said the group caused "significant damage" along a number of blocks and that more than 90 people were arrested and charged with rioting.
Before Inauguration Day, the DisruptJ20 coalition, named after the date of the inauguration, had promised that people participating in its actions in Washington would attempt to shut down the celebrations, risking arrest when necessary.
Earlier in the day, as guests were going in to the ceremony, lines for ticket-holders entering two gates stretched for blocks at one point as protesters clogged entrances.
More demonstrations were planned for later in the day.
The demonstrations won't end when Mr Trump takes up residence in the White House.
A massive Women's March on Washington is planned for Saturday. Christopher Geldart, the District of Columbia's homeland security director, has said 1,800 buses have registered to park in the city Saturday, which could mean nearly 100,000 people coming in just by bus.