Himself the son of a convicted felon, Kushner temperamentally is the polar opposite of his mercurial father-in-law and has only spoken once on an open microphone to the media since Trump began his candidacy in 2014.
Kushner owns a highly indebted real estate portfolio of his own, and his creditors include Deutsche Bank, which closed a much-needed $285 million loan right before election day (details here). Shortly thereafter, Deutsche Bank admitted to laundering more than $10 billion for Russian organized crime and other shadowy characters (details here).
Kushner has also been involved in real estate deals with Russians now being investigated for other money laundering endeavors (details here).
Kushner is also reviled by at least two former Trump White House officials known to be speaking with Mueller's team: Steven Bannon, the President's former senior advisor, who has spoken to investigators for more than twenty hours and also Michael Flynn, the President's first National Security Advisor. The latter has pleaded guilty and is cooperating with federal prosecutors. Vox reported in December with an article that speaks for itself (link here) that's titled "Why Michael Flynn’s plea deal could be really bad news for Jared Kushner."
Russia may not be the only one that is playing Kushner for its own benefit and against the United States. Last month, The New Yorker published a longer article about how Chinese interests may be manipulating Kushner in meetings barred to State Department and other US officials (link here).
A number of pundits have speculated Kushner is one of the more likely individuals in Trump's orbit to be indicted by Mueller's prosecutors. If he does so, and his father-in-law pardons him, that would almost certainly trigger a constitutional crisis.
That is, unless Republicans in Congress do nothing. If that happens, it will be one of the darkest days in American history.