On a day that his former campaign chairman, Paul Manafort, was convicted of financial fraud and Mr. Trump’s longtime lawyer and fixer, Michael D. Cohen, pleaded guilty to campaign finance violations that he said were directed by Mr. Trump himself, the president mostly steered clear of those subjects.

But the rally offered a vivid tableau of an extraordinary period in Mr. Trump’s already tumultuous tenure. The president is growing more defiant by the day even as the scandals appear to pose an increasingly serious threat to him, embarking on a cross-country tour in an urgent push to bolster his party’s chances of keeping control of Congress.

It was Mr. Trump’s sixth visit to West Virginia, and the leading edge of an intensive effort in which officials say he will headline rallies intended to stoke Republican enthusiasm and hold fund-raising events to stock the party’s campaign coffers. The state is home to Senator Joe Manchin III, who is facing a competitive race for re-election despite breaking ranks with his party and becoming the first Democrat to meet with Judge Brett M. Kavanaugh, Mr. Trump’s pick for the Supreme Court.

As Mr. Trump made his way to Charleston on Air Force One, news of Mr. Manafort’s conviction and Mr. Cohen’s plea dominated Fox News on the in-flight monitors. The president touched only glancingly on the issue in front of his enthusiastic crowd and never named either man. But he did denounce “fake news and the Russian witch hunt,” and taunted the team run by Robert S. Mueller III, the special counsel, which secured the convictions against Mr. Manafort.

“Where is the collusion?” Mr. Trump shouted as his supporters cheered. “You know, they’re still looking for the collusion. Where is the collusion? Find the collusion.”