Right, which is why I don't think he will have the goods to show any direct connection between Trump, collusion or obstruction. Otherwise, I see no reason why she comes out and says this now.
You must mean other than the obstruction that he admitted to on 60 minutes a year or so ago.
There is already enough impeachable stuff out there, especially if you go by 1990's standards. But, impeachment is a political process and Pelosi has concluded that impeachment would not politically expedient at this time. If Trump wins the 2020 election and the Dems keep the house, impeachment will be back on the table. The one thing I think you can probably speculate here is that the Dems have decided that there is not enough on Pence to take the whole administration. They don't want to take out Trump only to give Pence an 18 month audition for the White house.