Q: To prove damages in my legal malpractice case, do I have to prove that I could have collected on a judgment against the defendant in the underlying case if I had won?
There are no damages to the extent it is proven that an award in the underlying case could not have been collected, because under those circumstances the client was not really damaged (no harm, no foul).
However, in Washington, the issue is an "affirmative defense" for the defendant lawyer to plead and prove that the amount sought could not have been collected. Otherwise, it is presumed that, for instance, a judgment in the underlying matter would have been fully collectible. Schmidt v Coogan, 181 W2d. 661, 335 P.3d 424 (2014).
Oregon is also friendly to plaintiffs in this area, but does not go quite so far as Washington. In Oregon, the plaintiff must still come forward with "some evidence" to support collectability, and then the burden of proof or persuasion shifts to the defendant to prove that the amount would have been uncollectible. Ridenour v Lewis, 121 Or App 416, 854 P.2d 1005 (2002). However, In Ridenour, the court held that some evidence as to the likely amount of an underlying judgment (irrespective of collectability per se) satisfied this test, so the standard appears to be lenient for plaintiffs.