"It is the interest of two congressional committees, functioning under the authority of a resolution of the House of Representatives authorizing the subpoenas at issue, to obtain information on enforcement of anti-money-laundering/counter-financing of terrorism laws, terrorist financing, the movement of illicit funds through the global financial system including the real estate market, the scope of the Russian government’s operations to influence the U.S. political process, and whether the Lead Plaintiff was vulnerable to foreign exploitation," they continued.
Sounds impressive, but it reads like a complete load of crap to me as a lawyer. There isn't any suggestion or evidence that Trump's personal tax returns have anything to do with any of that. Law
enforcement is expressly not the function of Congress, and if there was a reasonable suspicion of criminal behavior, that would have to come from a prosecutor. The Mueller investigation examined tax returns in detail looking for exactly those kind of unlawful activities, and ended up prosecuting only Manafort. No hint of illegality on Trump's part.
What this is really all about is something entirely different. They want to get those tax returns so that they can be leaked -- illegally -- into the public domain. That's it.