I've never gotten involved in a Sanders based thread.

[George II]

5. I just don't understand the delay, it's been looming for almost three years now....

At least four other candidates have released current tax returns at the time of their last election or in preparation for this election:

Kamala Harris - 2015 when she ran for Senate in 2016, no doubt will shortly add to that
Cory Booker - 15 years when he first ran for Senate in 2013, no doubt will shortly add to that
Kirsten Gillibrand - 11 years released prior to even announcing her candidacy
Elizabeth Warren - 10 years released prior to even announcing her candidacy (actually 8 months ago)

Each of these are "new" presidential candidates and have already released tax returns. But the one candidate who has ostensibly been running for 3 years has only released one tax return, and that was from two years prior to his last candidacy (not the most current at the time)

The longer it goes on the worse it looks.