Of course, the ties between Trump and the Russian autocrat's government go further than just Manafort. The candidate himself has repeatedly praised Putin and given contradictory statements about his relationship with the foreign president, and Trump's team includes other advisers with Russian connections.
Take Carter Page, a Trump foreign policy adviser, for example. On Friday, Yahoo News published a report, which has not yet been independently verified by MSNBC or NBC News, that said U.S. intelligence officials are "seeking to determine whether [Page] has opened up private communications with senior Russian officials -- including talks about the possible lifting of economic sanctions if the Republican nominee becomes president."
Pointing to the report, Tommy Vietor, a former National Security spokesman for President Obama, suggested Trump may very well be "an unwitting Russian agent."
CNN's Jake Tapper asked Trump's campaign manager, Kellyanne Conway, about the allegations. Conway didn't comment on the accuracy of the reports, but instead argued that Carter Page has no role on Team Trump.
TAPPER: He is not part of the campaign anymore?
CONWAY: No, he's not. He's certainly not part of the campaign that I'm running.... And I also will say, if he's [engaging in back-channel communications with Russian officials], he's certainly not doing it with the permission or knowledge of the campaign, the activities that you described.... He is certainly not authorized to do that.
In March, for example, Trump provided some names of his top foreign-policy advisers to the Washington Post -- and Carter Page was the second name he mentioned.
It's certainly possible that Trump and Page parted ways at some point since, but the campaign never made any announcements to that effect, and given the seriousness of the allegations, Trump should probably explain when and why he stopped taking Page's advice (if, in fact, Trump has stopped taking Page's advice).
Not surprisingly, all of this has caught the attention of Hillary Clinton's campaign, which unveiled a new ad over the weekend about Trump's Russian ties and his secret tax returns.
In a normal year, with a normal candidate, this is the sort of controversy that would rock a campaign.