US President Donald Trump likes to boast that he hires only the best people. But his personnel choices keep coming back to haunt him.

One of the people Trump hired for the White House was working as a foreign agent while advising him during the election. His campaign chairman caught the Justice Department's attention for similarly surreptitious work. And a third campaign adviser was reportedly surveilled by the FBI as part of an investigation into whether or not he was a Russian spy.

The tales of Michael Flynn, Paul Manafort and Carter Page -- none of whom still work for Trump -- have created a steady drip of allegations that have clouded Trump's early presidency and raised persistent questions about his judgment.

At worst, Trump's personnel picks appear to have left his campaign -- and perhaps his White House -- vulnerable to the influence of foreign powers.  At best, they expose the long-term implications of his understaffed and inexperienced campaign organization and undermine his promises to surround himself with top-notch talent.

"Vetting new hires is standard procedure for presidential campaigns for exactly this reason," said Alex Conant, who advised Sen. Marco Rubio's 2016 presidential campaign. "Every employee is also a potential liability on a presidential campaign."

Manafort, Flynn and Page have indeed become political liabilities for Trump that he can't shake in the White House. All three are being scrutinized as part of the FBI and congressional investigations into whether Trump associates helped Russia meddle in the 2016 election. The president has denied any nefarious ties to Russia and says he has no knowledge that his advisers were working with Moscow during the election.

The president's culpability appears greatest with Flynn, a retired US Army lieutenant general who traveled with Trump frequently during the campaign and was tapped as national security adviser after the election.

Flynn had been lobbying for a company with ties to Turkey during the 2016 election and even wrote an editorial on behalf of his client that was published on Election Day.

"No one expects them to do the equivalent of an FBI background check, but a simple Google search could have solved a lot of these problems," Dan Pfeiffer, who served as senior adviser to President Barack Obama, said of Trump's team.

After Trump's victory, Flynn's lawyers alerted the transition team that he may have to register as a lobbying for a foreign entity, according to a person with knowledge of those discussions. The White House hired him anyway.

After the inauguration, Flynn's lawyers told the White House counsel's office that the national security adviser would indeed have to move forward with that filing. (AP)