Mr. Trump has been the meteorologist in chief, adding constant weather updates to a usual weekend of tweets attacking his enemies and retweeting bits of praise.

If the president did not originally inspire the gunman, he has brought into the mainstream polarizing ideas and people once consigned to the fringes of American society.

Democratic leaders say African-Americans are deeply engaged in this election, but President Trump is also targeting them with Facebook ads. How they react may well determine his future.

Mr. Biden, the front-runner, was confronted over his record on health care and criminal justice, and this time not just from Kamala Harris.

Tonight’s lineup featured 10 candidates including the former Vice President Joe Biden, Senator Kamala Harris of California and Senator Cory Booker of New Jersey.

Moderate underdogs kicked off the Detroit debates by targeting the top candidates with charges of “wish-list economics” and “impossible promises” on health care.

The CNN debate was a clash over health care with moderates along the edge throwing firebombs on the electability of progressives with the boldest policy plans.

House Democrats are moving aggressively to defend their majority, and rushing to protect the seats they hold in districts that supported the president in 2016.

The escalation rattled markets and thrust the world’s two largest economies, which had seemed on the brink of resolving their differences, back into confrontation.

The United States and China escalated their trade dispute on Monday as Beijing announced higher tariffs and the Trump administration prepared to tax all Chinese imports.

The president asserts that there is “no reason” Americans will pay tariffs, but economists and his own advisers say otherwise.

President Trump’s decision to renew his trade war with China could inflict lasting damage on the American economy, but the ultimate impact depends on how far the president takes the fight.

With aides enveloping him, Mr. Biden has not blurted anything out that delights his rivals or reinforces his image as America’s there-he-goes-again relative.

The president, in a series of tweets, said a prolonged trade war would be good for America even as negotiators returned to the table.

The House Judiciary Committee voted to hold Attorney General William P. Barr in contempt after President Trump asserted executive privilege over the full Mueller report.

Lawmakers plan to act despite a Justice Department threat to ask President Trump to invoke executive privilege over the Mueller report material they want to see.