SoloD
As you allude to, Mr Corbyn has spent his political life supporting international republican and/or revolutionary groups, including the late Venezuelan President Chavez (the current President Maduro’s mentor and predecessor), who first tried an unsuccessful coup in the early 1990’s, but on release from prison a few years later he founded a political party, and then took the Presidency ‘democratically’.
Indeed, around the time Chavez was trying to overthrow the Venezuelan regime, our ‘spooks’ thought they’d look into Mr Corbyn’s political activities, but that could have been more to do with his association with the old military wing of Sinn Fein around those times, attending numerous meetings, using one such event in 1988 to attack the Anglo-Irish Agreement, the precursor of the peace process.
“MI5 opened file on Jeremy Corbyn ‘to check if he was a terror threat’”
And regarding Israel, clearly Inviting Hamas and Hezbollah reps here and calling them ‘friends’, would raise more than a few security services eyebrows, as well.
Mr Corbyn (and Mr McDonnell) are proud of their ‘revolutionary’ pasts, as still support in one way or another many of those in past ‘struggles’ against an oppressor of sorts, as wasn’t that why the latter was recently trying to organise mass marches on Westminster to ‘overthrow’ the current government?
How often do you hear that as a political solution in non banana republics? 
Clearly you can take off a silly cap, trim down a beard, put on a pressed suit, white shirt, and red tie, but after 30-odd years, once an active revolutionary supporter, always a revolutionary supporter.
But I thought all that was the recent attraction.