Silicon Valley’s tech titans, under siege by federal regulators and lawmakers seeking to rein in their influence, are expected to face forceful new challenges to their power as the Democrats assume control of the White House and both houses of Congress. High on the Democrats’ agenda, policy experts said, are changes to antitrust law that could make it easier to block mergers or force companies to modify how they do business.

Frustration over how President Trump and his supporters used social media platforms to foment the chaos on Capitol Hill on Wednesday also could bring new energy to efforts by lawmakers to force tech companies to more closely moderate content on their sites. Some prominent Democrats blamed Trump’s posts for inciting the violence on Twitter and elsewhere.