Time for impeachment
There is now plenty of evidence that President Trump used the power of his office to withhold congressionally appropriated military aid to Ukraine.
He also used Rudolph Giuliani and ordered his staff to secretively withhold White House visits from the Ukrainian government. The President withheld these things from Ukraine until he received something he wanted, an investigation into one of his domestic political opponents. It is a federal crime for a public official to corruptly demand, seek, receive, accept, or agree to receive or accept anything of value in exchange for being influenced in the performance of an official act. President Trump committed this crime and should be impeached.