It doesn't matter if they wanted them in 2017. They are impeaching him NOW. They are entitled to them NOW. But even before the impeachment, the law that House committees can obtain the President's tax returns has no exceptions. It says "shall". It does not say "shall if the President allows it" or "shall if it's for a legislative purpose". And besides, they already listed several legitimate legislative purposes. Just claiming it's political is nonsense: Everything the Congress or President does is political. It's call Checks and Balances.

In 2016, the people voted and Trump won. That has to be honored. In 2018 the people voted and they made the House Democratic. That has to be honored, too.