However, according to Findlaw.com, this clause is not effective on any criminal charges whatever.
This clause is practically obsolete. It applies only to arrests in civil suits, which were still common in this country at the time the Constitution was adopted. 376 It does not apply to service of process in either civil 377 or criminal cases. 378 Nor does it apply to arrest in any criminal case. The phrase ''treason, felony or breach of the peace'' is interpreted to withdraw all criminal offenses from the operation of the privilege. 379
They mention WILLIAMSON v. U.S., 207 U.S. 425 (1908) as a case that stated that Senators and Congressmen can be arrested for anything actually criminal.
The article was designed to prevent partisan judges from issuing writs, including civil writs, which would prevent someone from being able to vote on a bill.
Even if the clause construed literally, Senator Craig's misconduct was a "breach of the peace."
The Minnesota statute he was charged under was 609.746 INTERFERENCE WITH PRIVACY, a law which punishes Peeping Toms for peeping, punishes people who install hidden cameras in tanning booths, and is designed to keep men from peering over or reaching under a bathroom stall occupied by another man, who may simply want to be alone with his thoughts. Thus, a "breach of the peace."
So what Larry Craig was claiming when he showed the arresting officer his business card was not "Senatorial immunity" which has some limited actual existence under the Constitution, but corrupt special privilege, which unfortunately is fairly common—see Beltway-itis: When Politicians Attack, by Michelle Malkin, just the other day.
Anyhow, Senator Craig, even before this scandal, wasn't much of an asset to either the Republican Party or the rule of law as far is immigration reform is concerned.
In 2003, a reader forwarded an LA Times story about Senator Craig's "bipartisan" cooperation with Ted Kennedy over "undocumented" workers with the words ”With Republicans like this, who needs Democrats?”
This latest incident just reinforces that point.