Let’s start with Paul Manafort, Trump’s campaign manager.
Manafort has a long history of working as a lobbyist for unsavory foreign leaders, including Zaire’s Mobutu Sese Seko and the Philippines’ Ferdinand Marcos. Most notably, Manafort worked as a political adviser for former Ukrainian President Viktor Yanukovych for years, masterminding his electoral victory in 2010. Yanukovych was a Kremlin stooge, one who (per the New York Times) paid Manafort millions between 2007 and 2012. Around that same time, Manafort also appears to have had links to Russian energy sector interests.
Trump’s foreign policy team, too, appears to have ties to Russia or a pro-Russian slant. Michael Flynn, a Trump adviser and former head of the Defense Intelligence Agency, was rumored to be on Trump’s VP shortlist. Flynn is currently a regular guest on RT, Russia’s English-language propaganda outlet. When he attended RT’s 10th anniversary party, he sat at the head table with Putin himself.
Carter Page, another Trump foreign policy adviser, has served as an adviser for Gazprom, Russia’s state-run energy corporation. As recently as March 2016, he said he owned shares in the company. "Page has defended Russia with relish," Slate’s Franklin Foer writes. "He wrote a column explicitly comparing the Obama administration’s Russia policy to chattel slavery in the American South."
You can see where people get the impression that the Kremlin might wield some direct influence over Trump: Many of his key advisers have business interests that tie back to the Russian state.
Interestingly, so does Trump himself. We can’t be sure exactly how much, as Trump refuses to release his tax returns. But Trump’s own son, Donald Trump Jr., said in 2008 that "Russians make up a pretty disproportionate cross-section of a lot of our assets."
...
In 2013, Trump found a new Russian partner for a Moscow real estate project, Aras Agalarov, an Azeri-born real estate developer who is sometimes called the "Trump of Russia" for his tendency to emblazon his name on his development projects.
The Agalarovs are wealthy developers who have received several contracts for state-funded construction projects, a sign of their closeness to the Putin government. Shortly after the pageant, Putin awarded the elder Agalarov the "Order of Honor of the Russian Federation," a prestigious designation.\
...
Instead of picking advisers from the anti-Russia neoconservative camp, who dominated GOP foreign policy before Trump, he has drawn some of the most pro-Russia people around. Trump sees Russia as a hot market, and has chosen to get into bed with suspiciously pro-Kremlin figures. He sees Putin as a model leader, not a disturbing authoritarian.
All of this suggests that Trump has thought a fair amount about Russia-related stuff, and come down on the Russian side. Trump’s skepticism about NATO and support for Russia’s intervention in Syria, then, are not incidental parts of his platform. They reflect the candidate’s actual worldview, and likely predict how he would act in office.
... Not to mention Trump supporting Russia's annexation of Ukraine's Crimea region. Sure, if that one Ivanka->Deng->Putin/Abramovich link existed in a vacuum you'd have a good case that it's merely, "guilt by association", but in this case, that's not the main story - it's just another sign of how these right-wing oligarchs are all connected worldwide. And that's a threat to American sovereignty.
Romney directly plugged his family's investment in rip-off private degree mill
Full Sail "University" during the 2012 election. But that
clearly corrupt action seems positively
quaint and charming compared to the types of investment conflicts of interests that the Trumps have.
EDIT: the most charitable analysis I can give is that the Trumps have a massive amount invested in Russia, and saying or doing anything anti-Putin jeopardizes those investments. So it's not so much guilt-by-association as it is a
massive conflict of interest, which has lead to Trump attracting to his campaign similarly pro-Russian types, or at the least preventing anyone vocally anti-Putin from being part of his inner circle of advisors. If he can't say/do anything against Putin during the election campaign because of how that would affect his investments (whether he wins or loses), then how is he going to govern, when Putin can effectively cut his economic balls off if he takes a strong stand on Russian aggression?