Donald Trump, clearly angered by news reports that he has grown depressed and sullen over his fading presidential prospects, has issued some of his sharpest attacks on the media.

"I am not running against Crooked Hillary Clinton," the Republican presidential candidate said in a speech late Saturday in Fairfield, Connecticut. "I'm running against the crooked media."

Trump seemed particularly upset with a New York Times article that quotes unnamed associates of his as saying that in private "his mood is often sullen and erratic." Republicans close to his campaign were quoted as saying he was "exhausted, frustrated and still bewildered" by the political process.

The real estate tycoon returned to his message on Sunday, tweeting: "My rallies are not covered properly by the media. They never discuss the real message and never show crowd size or enthusiasm."

Trump has complained for months about media coverage. He has stripped a long list of news organizations -- including the New York Times, Buzzfeed, Politico and the Washington Post -- of their credentials, and vowed that as president he would make it easier to sue news outlets.

But media monitors say he has received more extensive coverage than any candidate in years.

Paul Manafort, the Trump campaign chairman, also pushed back against the media during an appearance Sunday on CNN.

"Contrary to the New York Times's nameless sources story, the campaign is moving forward and very strong," he said. "We raised over $132 million in the last two months."

He noted that Trump had visited key battleground states such as Pennsylvania, Ohio and Florida repeatedly and was "starting to get traction in those states."

However, recent polls have shown Trump's numbers sagging badly in those battleground states, notably hurt by his critical comments about the Muslim parents of a fallen US soldier, and what some saw as his suggestion that "Second Amendment groups" -- gun lovers -- take their dislike for Clinton into their own hands.

Manafort repeated the Trump claim that his Second Amendment remark was meant purely as an exhortation to vote.

But even one of Trump's top advisers, Senator Jeff Sessions of Alabama, conceded Sunday that the candidate needed to communicate "more effectively."

"He's got to wrestle in his own heart, how does he communicate who he is, what he believes, the change he thinks he can bring to America," he said on ABC.

"He does need to communicate -- and I think he can -- more effectively."

The CNN interviewer also asked Manafort about mounting pressure on Trump to release his tax returns after Clinton released hers on Friday.

The channel broadcast video of Trump urging Mitt Romney, the Republican candidate in 2012, to release his returns at the time, saying, "If you didn't see the tax returns, you would think there is almost, like, something wrong."

Manafort repeated Trump's explanation that he is under audit by the Internal Revenue Service.

"When that's completed, he'll release the returns," Manafort said, adding that Clinton's returns showed income coming from "people who benefited from her State Department term as well," referring to her time as secretary of State.

"I haven't seen stories on that yet."