Republican nominee Donald Trump has ripped into House Speaker Paul Ryan as a “weak and ineffective” leader.
Mr Trump unleashed an attack on Mr. Ryan after the highest-ranking Republican said he would not defend the candidate.
Mr Ryan is the latest Republican not to back Mr. Trump after a 2005 video emerged showing him making obscene comments about groping women.
Renewed party divisions over Mr Trump come as a new poll shows him 11 points behind his rival Hillary Clinton.
The PRRI/Atlantic poll released two days after the second US presidential debate suggested Mrs Clinton holds a 49-38 lead over her opponent.
A video released on Friday revealed Mr Trump describing how he had sought to have sex with a married woman and making other sexually aggressive comments about women.
The controversy prompted dozens of Republican lawmakers to rescind their support for Mr Trump less than a month before election day.
On Monday, Mr Ryan told fellow House Republicans he would focus on congressional elections to ensure Republicans could maintain legislative control.
Mr Trump fired back in a string of tweets, saying the “shackles” had been removed, allowing him to “fight for America the way I want to.”
It is so nice that the shackles have been taken off me and I can now fight for America the way I want to.
— Donald J. Trump (@realDonaldTrump) October 11, 2016
Paul Ryan should spend more time on balancing the budget, jobs and illegal immigration and not waste his time on fighting Republican nominee
— Donald J. Trump (@realDonaldTrump) October 10, 2016