Democrats targeted Morella, a liberal Republican, for defeat last year when Maryland Gov. Parris Glendening and Democrats in the state Legislature redrew the 8th District.

CNN: Incumbent Morella defeated in Maryland

He and Rivers, who has served four terms in the House, were thrown into a race together after the GOP-controlled Michigan Legislature redrew the lines of congressional districts during reapportionment.

CNN: Dingell survives Michigan primary

Running as an independent allows Traficant to avoid a primary race against eight-term Democrat Rep. Tom Sawyer, who was placed in the same district as Traficant when the Republican-controlled Ohio legislature redrew the boundaries.

CNN: Traficant files for re-election as independent

If the Republicans do seize control of Congress at this year's mid-terms, an important part of the reason will be the ways in which their state-level legislators redrew the lines in big states like Texas, Ohio and Florida after the census of 2000.

ECONOMIST: Electoral boundaries in America