His pension amount of $4,982 is fully taxable. His social security of $46,213 is 85% taxable, so he does dodge the tax on about $5K there.
Sanders doing so well on those small donations is a statement the elite best not ignore. Trump, on the other side of the coin, gets some small "thank you" donations. Instead he sells merchandise. It would be interesting to know how many folks buy merchandise and what was the average price of each purchase. I find it fascinating and totally consistent that Trump would rather sell me a tee shirt for $25 than have me send a $25 donation.