WASHINGTON - Republican presidential hopeful Donald Trump, looking to revitalize a White House bid that has stumbled in recent days as he looks to a November showdown with Hillary Clinton, on Monday dumped his controversial campaign manager.

Trump, 70, has recently taken a hit in the national polls and sparked outrage with comments about Muslims in the wake of the Orlando gay club massacre. With less than a month to go before the Republican convention, changes were inevitable.

After weeks of rumors about dissent within his camp over how best to take on Clinton, the presumptive Democratic nominee, the hammer came down Monday when campaign manager Corey Lewandowski left Team Trump.

“Corey Lewandowski will no longer be working with the campaign,” spokeswoman Hope Hicks said in a statement. “The campaign is grateful to Corey for his hard work and dedication and we wish him the best in the future.”

Trump’s team did not specify the terms of Lewandowski’s departure.

Lewandowski was credited with Trump’s initial breakthrough in the primaries, but he has recently been sidelined, with more experienced political operatives like Paul Manafort, who will now lead the campaign, being given more influence.

Lewandowski courted controversy earlier this year over a March run-in with a reporter at a Trump rally. She accused him of roughly grabbing her, leaving bruises, but he denied that account. Florida prosecutors opted to drop all charges.

According to New York magazine, Trump’s adult children - Donald Jr, Eric and Ivanka - pushed for Lewandowski’s ouster, saying he was not up to the job in the run-up to November 8.

The Trump campaign is “deeply troubled,” said political analyst Larry Sabato, head of the Center for Politics at the University of Virginia.

“This is a campaign that is underfunded, that isn’t properly organized. The convention itself is questionable in terms of what it’s going to produce.”

Sabato added: “The Clinton campaign is simply light years ahead of the Trump campaign.”

Last week, Clinton - who has far better funding thanks to supporters and big donors - launched a media blitz of ads attacking Trump in eight key states - Colorado, Florida, Iowa, Nevada, New Hampshire, North Carolina, Ohio and Virginia.

The ads will run for six weeks, until the party conventions - the Republicans meet from July 18-21 in Cleveland, and the Democrats convene in Philadelphia from July 25-28.

Campaign volunteers for the 68-year-old former secretary of state, who is seeking to be America’s first female president, will go door-to-door next weekend to get out the vote.

Such ground work takes time to organize, but Trump’s campaign is planning to outsource it to the Republican party - a task it normally does not perform.

After sewing up the Republican presidential nomination in early May, Trump had closed the gap with Clinton in the polls.

But since then, Clinton has dispatched rival Bernie Sanders and found her rhythm on the trail in blasting Trump. Result - she now has a nearly six-point lead over the billionaire, according to an average of opinion polls by specialist website Real Clear Politics.

Clinton, relying on her deep experience in foreign policy, has repeatedly drilled home the idea that Trump is “temperamentally unfit” and unqualified to lead.

Trump has repeatedly promised to tone down his rhetoric and lead a more understated campaign, but has not done so, much to the chagrin of worried Republican leaders.

His attacks on a federal judge of Mexican descent who is presiding over cases involving Trump’s defunct online university, alleging bias because of his heritage, have shocked some Republicans, and revived the slim hopes of some anti-Trump Republicans that someone else could be the nominee.

Trump’s decision to head to Scotland this week to open up a new golf course, instead of remaining on the campaign trail, has also turned heads and heightened fears about his ability to focus on the White House race.

All that could spell chaos for a Republican convention that is meant to highlight unity - the party is certainly laboring to project that image, and Apple’s decision to drop out as a sponsor over Trump won’t help.

But Trump remains unfazed, telling MSNBC at the weekend: “We really haven’t started. We start pretty much after the convention.”