Republican members of the House Intelligence Committee abruptly ended its investigation into Russian collusion this week, concluding that they could find no basis to believe the president or his allies did anything wrong. They also broke with an intelligence community consensus that the Russians meant to help Mr. Trump.

Their finding came despite the fact that a special counsel continues a wide-ranging investigation that could produce different results. But it cheered Mr. Trump and the White House and reflected a view by many House Republicans that their own inquiry was unfairly undermining the president — and by extension themselves — and had gone on long enough.

The decision drew a strong rebuke from Democrats, including Senator Chuck Schumer of New York, the Democratic leader.

“Sadly, far too many of our friends on the other side of the aisle have been more concerned with protecting the president politically than defending our democracy,” said Mr. Schumer, who also noted the White House has refused to impose new sanctions on Russia that were ordered by Congress but has drawn no Republican criticism for its inaction. “From the top on down through the rank and file,” Mr. Schumer said, “the Republican Party that used to roar like a lion against Russia now squeaks like a mouse.”

On gun control, the president only days ago seemed poised to offer a drastic departure from Republican orthodoxy on gun issues by pushing for more comprehensive background checks, raising the age limit to buy weapons and encouraging members of his party to be bold about breaking with the National Rifle Association. But instead of using presidential clout to push his party in a new direction and put lawmakers on the spot, the White House backed off and embraced more ideas more compatible with the N.R.A. while establishing a commission to explore other alternatives.