"We don't know what's going on here, and Donald won't tell us," the spot concludes. "We'll let you guess."
To be sure, a victory for Trump would augur a radical shift in US foreign policy towards Russia. The United States would be much friendlier toward Putin and much more accommodating of his international agenda.
Trump has surrounded himself with people who are sympathetic to Putin. Paul Manafort, the chairman of Trump's campaign, also advised former Ukranian President Viktor Yanukovych, who was aligned with Putin. Carter Page, one of Trump's advisers on foreign affairs, has openly praised Putin and criticised Western sanctions on Russian officials.
Trump himself has praised Putin, as well, and has also called for the United States to retreat from its responsibilities in Nato - which would probably increase Putin's influence in the region.
At this point, however, there is no evidence that anyone in the Trump campaign has a direct connection with the Kremlin, as Clinton's spot insinuated.
The Clinton campaign did not immediately respond to a request for comment.
There's also no evidence that Trump himself has business relationships with people in Russia that would cause a conflict of interest if he were elected. Trump has been seeking business in Russia for a long time, without any visible successes.
"The fact that Trump, after so many attempts and with such warm intentions towards the country, was not able to build anything in Russia - when Ritz Carlton and Kempinski and Radisson and Hilton and any number of Western hotel chains were able to - speaks to his abysmal lack of connections to influential Russians," Julia Ioffe wrote in Foreign Policy. "If Trump truly was in bed with Putin, there would be a Trump Tower in Moscow by now, if not several."
Trump's positions on foreign policy and his evident fondness for Putin are consistent with his other positions. He believes in putting US interests first, even ahead of those of close foreign allies. He has expressed admiration for authoritarian leaders around the world, not only in Moscow. A conspiracy theory is not necessary to explain Trump's views on Russia.
All the same, the Clinton campaign has invited voters to come up with one, Uscinski said. He compared the rhetoric in the advertisement to Trump's strategy of stating a few facts and asking leading questions without clearly stating any accusations that could be refuted.
"There's something going on," the New York businessman is fond of saying.
Uscinski said the advertisement was politically savvy. Trump's supporters are more likely than other Republicans to endorse conspiracy theories, polling has found, so an advertisement that appeals to that worldview might prove successful.
For instance, Trump's supporters are more likely than supporters of other Republicans to believe that Clinton knew that the US diplomatic compound in Benghazi would be attacked and chose not to act.
They are also more likely to believe that President Barack Obama is hiding something about his early life. Both cases arguably demonstrate the anxiety that many Americans have about some kind of foreign agent becoming president, and Clinton's new advertisement addresses that anxiety directly.
In that respect, the spot challenges a crucial aspect of Trump's appeal to voters.
"The strategy behind the ad, I think, is absolutely beautiful for her," Uscinski said. "She's essentially undermining Trump's entire message, which is 'America first,' and by making him look like a pawn of some other country, all of a sudden his message is obliterated."
