He is declaring the Mueller investigation illegal. He will never submit to an investigation under oath. He has the Republican congress solidly behind him now and no matter what the Mueller investigation reveals they will declare it null and void. We are now in an ongoing state of obstruction of justice by the President and the Republican party. There is no legal remedy. The only remedy possible is Democrats taking the house of representatives in November. And even if they do win they may decide to do nothing and ride it out because of the political risks involved.