"The speaker is going to spend the next month focused entirely on protecting our congressional majorities," Ryan's spokeswoman, AshLee Strong, said in a statement.
The move -- highly unusual in US political history -- laid bare the seemingly intractable divisions now seizing the Republican Party with a month left before the presidential vote. Support for Trump among the GOP establishment, already weak amid disagreements over policy and tone, has now eroded to new lows.
In a conference call with members Monday morning, Ryan told lawmakers, "you all need to do what's best for you and your district," according to someone who listened to the meeting.
"He will spend his entire energy making sure that Hillary Clinton does not get a blank check with a Democrat-controlled Congress," said the person on the call -- an implied acknowledgment that Trump no longer appears able to capture the White House.
Reaction to Ryan's decision illustrates the schism currently splitting the Republican Party. A person who listened to the call said the reaction wasn't entirely positive -- and that Ryan's comments angered more conservative GOP members who believed the speaker was essentially conceding the presidential contest to Clinton.
And later on Monday Republican National Committee Chairman Reince Priebus reiterated his support for embattled GOP nominee Trump.
"Nothing has changed in regard with our relationship," Priebus said in a call with RNC committeemen. He said the Trump campaign and RNC are in full coordination.
Trump hits back
Trump responded to the House speaker on Twitter Monday, saying Ryan should focus on other policy areas instead of fighting with the Republican nominee.
"Paul Ryan should spend more time on balancing the budget, jobs and illegal immigration and not waste his time on fighting Republican nominee," Trump said.
At least eight members angrily pushed back at Ryan, saying the party needs to be united headed into November to keep the majority. One member, two sources on call said, pointedly told Ryan that the better Trump does in November, the better the House GOP will do.
"It's not rocket science," the member said.
Among the people who objected to Ryan: Rep. Billy Long of Missouri, a Trump supporter, Rep. Louis Gohmert of Texas, and Rep. Dana Rohrabacher of California.
Ryan's comments follow a Washington Post story out Friday
which revealed Trump made lewd and sexually aggressive comments in 2005 that were caught on a hot microphone. Trump apologized for those remarks at Sunday's debate, but dismissed them as "locker room talk" and pivoted to attacks on former President Bill Clinton.
But Ryan did make clear that he would no longer provide proactive support for his party's presidential candidate. A source said the speaker would campaign in 17 states and 42 cities this month.
A spokesman for Trump's campaign, Jason Miller, tweeted after the news broke, "Nothing's changed. Mr. Trump's campaign has always been powered by a grassroots movement, not Washington."
A Trump campaign source told CNN the campaign has told members of Congress from the beginning to focus on winning their seats, even if that means abandoning Trump because the campaign wants as big a Republican majority as possible come January.
Ryan spokesman Zack Roday said the speaker "made it clear on the call he's not conceding the presidential race."
Ryan under scrutiny
The speaker's actions in the aftermath of the lewd tape's release have been closely monitored given Ryan's initial reluctance to get behind Trump when he clinched the GOP nomination.
Dozens of fellow Republican lawmakers withdrew their support for Trump, many insisting he should withdraw from the race entirely. The defections came largely from Republican lawmakers facing tough re-election battles, including Sen. Kelly Ayotte. In the House, Rep. Jason Chaffetz said Trump should step aside.
Trump and Ryan were originally set to appear together in Wisconsin on Saturday. But Ryan rescinded his invitation after the new comments came to light. Over the weekend, his office remained largely quiet about how he would respond to the explosive reports about Trump's past behavior.
But on the call Monday, the message was unequivocal: Trump will no longer enjoy whatever political firepower Ryan could bring to the presidential race in its final stretch.