... The act of following the law should not be dependent upon the outcome.
The Constitution tells us that the House has the power of impeachment. During prior administrations in which impeachment was an issue, a committee was created to summon witnesses and to subpoena documents and other items (for example, tapes.) The committee then proposed specific articles of impeachment for the entire House. If a majority of the House voted to approve, (which it likely would today) the charges were sent to the Senate.
However, the Constitution requires a two-thirds majority in the Senate to remove the president, which would be unlikely to obtain in the current administration, given that the Senate is now Republican controlled. Democrats seem wary of this potential for impeachment failure. In 1998, after the House impeached Bill Clinton, a Democrat, his popularity actually increased. In the Senate, even some Republicans voted against convicting Clinton of the charges. Afterward, Democrats won seats in the midterms and Republican House Speaker Newt Gingrich left Congress.
If impeachment isnt likely to happen because of the make-up of the Senate, why bother going to all of the effort to do the work in the first place? Because the point of following the Constitution is not to obtain a particular outcome. Whether impeachment is likely to succeed in removing Trump from office is not the issue ...
https://thehill.com/opinion/white-house/445600-america-has-no-time-to-wait-for-impeachment