Could Trump sue Pelosi for malicious prosecution ? ...

[dogtag]

As the Impeachment clause is for removal of a sitting President,
which Trump clearly was not after he lost the 2020 election -
(fairly or not is beside the point). He lost and so as to ensure his
ineligibility for office in the future the clearly unconstitutional use
of the impeachment process initiated by Speaker Pelosi seems to
be a deliberate and criminal act. "No one is above the law" the oft
quoted slogan surely applies here ?

[Vern Humphrey]

No.

US Constitution, Article I, Section 6:

Section. 6.
Clause 1: The Senators and Representatives shall receive a Compensation for their Services, to be ascertained by Law, and paid out of the Treasury of the United States. They shall in all Cases, except Treason, Felony and Breach of the Peace, be privileged from Arrest during their Attendance at the Session of their respective Houses, and in going to and returning from the same; and for any Speech or Debate in either House, they shall not be questioned in any other Place.

They can't be sued or charged for what they do in Congress.