Donald Trump declared on Tuesday morning that he had been freed from “the shackles” of the Republican Party and would now campaign as he saw fit, furthering his split from the party he deemed disloyal to him.

In a series of messages on Twitter, the GOP presidential nominee said House Speaker Paul Ryan, also a Republican, was a “very weak and ineffective leader” who had given his candidacy “zero support.”

The outburst came after the unprecedented defection in recent days of dozens of Republican senators, congressmen and governors over a newly surfaced video from 2005, in which Mr. Trump boasts about making unwanted sexual advances toward women.

On Monday, Mr. Ryan told his conference he would no longer defend Mr. Trump nor campaign with him, and said his goal was to maintain Republican control of the House in November’s general election.

In his Tuesday tweets, Mr. Trump suggested the defections had made it easier for him to campaign as himself.