Trump whines about being left out of inquiry, but then turns down chance to participate - 2019-12-02
So Trump has declined Jerry Nadler's invitation to participate in the next phase of the impeachment inquiry, scheduled to commence this week, which isn't all that surprising since actually participating would undermine their argument that the inquiry was a sham for not allowing Trump to participate.
The key thing to realize about the White House's whiny posturing and ceaseless efforts to delegitimize the inquiry is that a suspect's due process rights are practically non-existent at the investigation phase, which phase we're still at, whether you're talking about a criminal investigation, grand jury proceedings, or an impeachment inquiry. Due process rights kick in after a charge, an indictment, or impeachment articles.
When Ken Starr investigated Bill Clinton, the investigation was conducted mostly in secret. Since the Attorney General is hopelessly compromised, the House is playing the role of Special Prosecutor and conducting its own investigation. It is not conducting a trial — the Senate performs that task.