Republican presidential candidate Donald Trump says the House of Representatives' Speaker Paul Ryan, the party's top elected official, should "not waste his time" opposing the party's nominee.
"Paul Ryan should spend more time on balancing the budget, jobs and illegal immigration and not waste his time on fighting Republican nominee," Mr Trump said in a post on Twitter on Monday.
Mr Ryan has distanced himself from the divisive business magnate, saying he will not campaign with Mr Trump nor defend him leading up to the election.
He told fellow Republican leaders in a conference call they needed to do what was best for them.
Mr Ryan says he wants to use the next 29 days to focus on preserving his party's hold on Congress.
Although he appears to no longer support Mr Trump, he has not officially withdrawn his endorsement.