You need to be clear here. With the House majority the dems have the ability to pass articles of impeachment. This is what is usually meant by impeach. But the senate is another thing. Since we have not seen the senate ever pass something that needs more than 60 votes, is is not likely that we will see a charge of impeachment ever lead to conviction. So absolutely, Mueller does not have enough to convince 67 senators to vote to convict. Of course this also means that they will have settled on a criminal act, which we also have not yet seen.