Those revelations made Manafort politically toxic. (Rick Gates, a longstanding Manafort aide who was also implicated in the stories, is moving to become the campaign’s liaison to the Republican National Convention, the campaign said.) But Manafort’s demise may have been driven by Trump’s floundering standing in polls as much as by the bad press. Trump, after all, likes to win, and he hasn’t been doing much of that recently.

Manafort’s term on the Trump campaign began in March, when he was hired to lead delegate-counting efforts. A veteran operative—Manafort cut his teeth working for President Gerald Ford in 1976, beating back a primary challenge from Ronald Reagan—he brought essential expertise to a Trump campaign that had proved adept at winning primaries and motivating a certain segment of the GOP base. Despite those wins, however, Trump was failing to place his own delegates at state conventions, and it appeared he risked a floor fight at the Republican National Convention.

Ultimately, Trump was able to lock up the delegates to avoid a floor fight, but his then-campaign manager, Corey Lewandowski, was fast becoming a liability. Although Lewandowski had gotten Trump that far, he seemed perhaps overmatched on the national scene, and moreover was garnering bad headlines for grabbing a Breitbart reporter at a rally in Florida, then claiming he had not done so, despite eyewitnesses and video footage proving it.

Manafort adeptly maneuvered himself into a promotion to campaign chairman in May. But he and Lewandowski feuded constantly, with Manafort pushing for a more moderate approach, following a more typical political playbook. Lewandowski, in contrast, argued for a more unorthodox “let Trump be Trump” strategy, pointing to its success in the primary. Finally, Trump fired Lewandowski in June, reportedly at the urging of his children and also of Manafort. For many observers, this marked a milestone in the Trump campaign, the moment when the candidate turned away from the motley bunch of amateurs he’d begun with and began to professionalize his campaign.

Any such illusions proved to be short-lived. Manafort was no more able to get Trump to stay on message than anyone else, and his attempts at moderation went nowhere. A classic example was Trump’s infamous tweet of himself eating a taco bowl on May 5, Cinco de Mayo. “I love Hispanics!” he wrote. Howard Fineman reported this week:

Manafort was in the office with other aides when a member of the family suggested they tweet a picture of Trump enjoying his “Mexican” lunch. Manafort politely suggested that this might be seen as condescending and cautioned against it. The tweet went out. Trump himself was delighted by the resulting controversy. “The people who were offended were people we wanted to offend,” he later said.

Trump stumbled through June and July in a pattern of occasionally straightening up and sticking to a teleprompter, only to return to his old ways with ad libs or ill-advised feuds. The Republican National Convention in late July was widely viewed as a bust: Not only was it poorly run and timed, it produced a small and ephemeral polling bump, and Gallup found that for the first time in more than 30 years, voters had a less positive impression of a candidate after the convention than before.