Republicans are complaining that House Speaker Nancy Pelosi is violating the U.S. Constitution by not forwarding the articles of impeachment to the Senate.
The reason is because she believes that Senate Majority Leader Mitch McConnell and the Republican majority are not taking the articles of impeachment seriously, which they have yet to do.
The Senate is required by the U.S. Constitution to hold an impeachment trial, which they show no sign of doing. A trial is where evidence is introduced, and witnesses are questioned. If necessary, if evidence and witness's testimony is not voluntarily provided and given, it necessary to subpoena the evidence and witnesses. McConnell doesn't want to subpoena evidence or witnesses.
This is not taking the articles of impeachment seriously and violates the U.S. Constitution.
Pelosi has a constitutional duty to ensure that the impeachment process is taken seriously, which is exactly what she is doing. If this means Trump is forced to run for reelection as impeached president, then so be it. No one is to blame but himself and the Republicans, but they, of course, will not take responsibility for this.