WASHINGTON — Representative Vance McAllister, Republican of Louisiana, under heavy pressure from House Republican leaders since he was caught kissing a congressional aide, announced Monday that he would not seek re-election to the seat he has occupied for only five months.

But Representative Michael G. Grimm, a two-term Republican from New York, appeared to encounter no such pressure as he faced a 20-count indictment on Monday for fraud, tax evasion and employing illegal immigrants.

The disparate treatment of the two House members pointed up an odd dichotomy that has emerged since the current Republican leadership came to power pledging a get-tough response on ethics issues.

If House members are caught up in sexual peccadilloes or other made-for-television acts, they have been driven from Capitol Hill posthaste. If the allegations are more complicated, they have largely been given a pass.