A Trump senior campaign aide confirmed to Fox News Monday morning that Lewandowski is no longer with the campaign.
It's unclear what specifically led to the shake-up. The high-profile departure of one of Trump's most senior and loyal advisers follows what was widely seen as a rough patch for the campaign.
Trump's polling numbers against presumptive Democratic nominee Hillary Clinton have slipped in recent weeks, and Trump has found himself caught up in several controversies over his own comments.
Lewandowski has been by Trump's side since the beginning of his unlikely rise to presumptive GOP nominee.
The move comes as Trump faces continued deep resistance from many quarters of his party concerned by his contentious statements.
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