1. Say the obviously impeachable conduct happened but isn't impeachable.
2. Say the constitutionally valid process is unconstitutional and seek to disrupt it.
3. Attack the integrity of the obviously honest chairman of the committee overseeing the impeachment process.
4. Try to prevent the numerous witnesses from giving evidence.
These are lame defences. The sort a guilty thug like Trump would employ.
They also tell you Trump cannot defend his behaviour using the law, reason, morality, or the interests of the United States.
He's going to be impeached. He will be tried. He ought to be removed, not only because he is guilty of everything he is charged with, but because Trump is a brown smear on the Republican brand, and removing him will begin the cleansing process.