Would in if-clauses #2

It's a simple "could if he would" verb matching.

However, the "if he was willing" can work as well.

It means the same as,

Trump can/it is possible for Trump to clear up all the suspicion about Russian bank/government loans if he will release his taxes like he once promised to do.

'could' and 'would' are used because the writer recognizes that the issue upon which he pontificates is a more speculative thing, so he uses "distant" modals to reflect that.

The 'would' could/can also mean as you have noted above, "his willingness".