[x]

I found this: The Clever Way Jefferson Davis Avoided Being Convicted Of Treason.

I can't say how valid it is. If it's true, the arguments seem pretty slippery.

Finding a jury in Virginia wouldn't have been impossible, but as a unanimous verdict was required, you could never be sure there wouldn't be one joker in the deck.

[Texas Mulerider]

In some circles, there wasn’t much appetite for trying Davis for treason anyway. Officials of the US government were afraid that Davis would prove that the South’s secession had been legal.

I'm dubious of Chase using the particular argument cited in the article, but who knows. The part of the article I quoted above dovetails with what we do know, which is that Chase warned the Johnson administration in June, 1865: "If you bring these (Confederate) leaders to trial it will condemn the North, for by the Constitution secession is not rebellion. Lincoln wanted Davis to escape and he was right. His capture was a mistake. His trial will be a greater one." (Foote, The Civil War, Vol. 3, p.762)