Representative John Tierney’s reelection bid this year looks far more difficult than it has in the past. Legal proceedings involving his wife, Patrice, have dragged on, generating a stream of potentially damaging headlines, and the congressman this time is facing a far more formidable opponent. Richard R. Tisei, a 49-year-old Republican real estate agent, is a moderate with 26 years in the State Legislature and the full backing of his party. And unlike Tierney’s last challenger, Tisei has run a major campaign before.