WASHINGTON -- His whirlwind foreign trip complete, President Donald Trump faces a slew of political and policy challenges at home and mushrooming inquiries into allegations that Russia meddled in the U.S. election and had improper dealings with his campaign and associates.

Mr. Trump returned to Washington late Saturday after a nine-day trip to the Middle East and Europe, his first trip abroad as president.

"Just returned from Europe," Mr. Trump tweeted early Sunday. "Trip was a great success for America. Hard work but big results!"

Just returned from Europe. Trip was a great success for America. Hard work but big results! — Donald J. Trump (@realDonaldTrump) May 28, 2017

Before heading home, he recounted what he called "home run" successes of his first foreign trip, as he addressed American troops stationed at Naval Air Station Sigonella in Sicily, Italy.

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Awaiting him at home were reports that his son-in-law and senior adviser, Jared Kushner, spoke with Russia's ambassador to the United States about setting up secret communications with Moscow during the presidential transition.

White House aides prepared for potential changes ahead, with the president mulling a staff overhaul amid frustrations over what he views as his communication team's failures to push back against allegations. A rally planned Thursday in Iowa was postponed due to "an unforeseen change" in Trump's schedule.

While overseas, Mr. Trump's longtime attorney, Marc Kasowitz, joined a still-forming legal team to help the president shoulder the intensifying investigations into Russian interference in the election and his associates' potential involvement. More attorneys with deep experience in Washington investigations are expected to be added, along with crisis communication experts, to help the White House in the weeks ahead.

"They need to quarantine this stuff and put the investigations in a separate communications operation," said Jack Quinn, who served as White House counsel for President Bill Clinton.

During the Monica Lewinsky investigation, the Clinton White House brought on a dedicated group of lawyers and a created a separate media operation to handle investigation-related inquiries so they didn't completely subsume the president's agenda.

"I think that was enormously helpful," Quinn said.

A GOP source close to the White House told CBS News that "the inside-outside effort needs to take a page from Clinton's operation when they were battling Monica Lewinsky."

"They had an internal mechanism to direct all calls and incoming [questions] to a crisis containment center, in order to use the communications office -- the White House press office -- as offense," the source said.

"At the same time, they had a surrogate operation to have their voices heard. That's what needs to happen on the reactive side," the source added.

As he mulls new additions and outside reinforcements, Mr. Trump has entertained bringing his former campaign manager, Corey Lewandowski, and former deputy campaign manager, David Bossie, formally back into the fold. Mr. Trump has been speaking to Lewandowski and Bossie, although it is unclear if they will play a formal role in the communications shakeup, CBS News' Jacqueline Alemany and Steve Chaggaris reported.

Lewandowski was Mr. Trump's first campaign manager, and Bossie served as deputy campaign manager.

Lewandowski's return would be a particularly notable development, given the fact that he was fired by Mr. Trump after clashing with other staff as well as Mr. Trump's adult children. Nonetheless, Lewandowski, who led the small team that steered Mr. Trump's primary victory, has the trust of the president -- an advantage that many of Mr. Trump's aides lack.

CBS News has confirmed a looming shakeup that is bound to eliminate some source of drama among staffers. Leakers of classified information at the White House have been identified and will be fired. Sources said that their terminations are being processed.

"You have no idea how paranoid it makes people," a White House official said of the rampant leaking.

The White House had hoped that Mr. Trump's trip abroad would serve as a reset, but attention on the Russia probe has only increased. Recently appointed special counsel Robert Mueller, a former FBI director, is starting off an investigation with a broad mandate that will allow him to probe both the possible Russian influence and whether Mr. Trump attempted to obstruct the investigation by firing FBI Director James Comey.

Heightening concerns for the White House, Comey is expected to testify before Congress after Memorial Day about memos he kept on conversations with the president that pertained to the investigation.

The White House also grappled with reports that Kushner proposed setting up a secret back channel between the Kremlin and the Trump transition team during a December meeting.

Citing a person familiar with the discussions, The Associated Press reports that Kushner spoke with Sergey Kislyak, the Russian ambassador to the U.S., about creating the secret line to make it easier to hold sensitive discussions about the conflict in Syria. The back channel was meant to connect Michael Flynn, who later became Mr. Trump's first national security adviser, with Russian military leaders, said the person, who wasn't authorized to publicly discuss private policy considerations and spoke on condition of anonymity.

Flynn was fired in February, officials saying he misled Vice President Mike Pence about whether he and the ambassador had discussed U.S. sanctions against Russia in a phone call.

Before departing Italy for the U.S., White House officials refused to address the reports about Kushner.

"We're not going to comment on Jared," White House Economic Council Director Gary Cohn told reporters in an off-camera press briefing Saturday. "We're just not going to comment."

President Donald Trump and first lady Melania Trump walk from Marine One across the South Lawn to White House in Washington, Saturday, May 27, 2017, as they return from Sigonella, Italy. Carolyn Kaster/AP

Other major issues await decisions by Mr. Trump. He tweeted that he would make a final decision next week on whether to withdraw from the Paris climate agreement, in which nearly 200 countries pledged to reduce their greenhouse gas emissions in an effort to combat global warming.

I will make my final decision on the Paris Accord next week! — Donald J. Trump (@realDonaldTrump) May 27, 2017

As a candidate, Mr. Trump vowed to pull out of the accord, which was negotiated during the Obama administration, claiming the deal would be economically disadvantageous to the U.S.

The search continues for an FBI director to replace Comey. Mr. Trump interviewed potential candidates and said he was "very close" to deciding on a replacement before he left for the Middle East. But one of Mr. Trump's short-list candidates, former Connecticut Sen. Joe Lieberman, withdrew from consideration, and the White House has been mum on other possibilities.

Mr. Trump's policy agenda has run into road blocks since he departed Washington. The Republican health care bill that narrowly passed the House faces an uncertain future in the Senate after a Congressional Budget Office analysis said it would leave 23 million more Americans uninsured by 2026.

The president will need to defend his budget plan, which was released while he was abroad and drew criticism for deep cuts to safety net programs.

Mr. Trump also has to decide soon on a Pentagon recommendation to add more U.S. and NATO troops in Afghanistan, as well as boosting reinforcement for the beleaguered Afghan forces. The Pentagon says it has about 8,400 troops in Afghanistan, about one-quarter of whom are special operations forces targeting extremist groups such as an Islamic State of Iraq and Syria (ISIS) affiliate. The Pentagon has asked for 3,000-5,000 more personnel, CBS News' Elizabeth Palmer reports.