Complex sentence: Will stated that Barr could have a similar effect on the election as Ralph Nader in 2000 yet described this effect as a "punishment" to presumptive Republican Party nominee John McCain for his co-sponsorship of the Bipartisan Campaign Reform Act of 2002, which Barr opposed.
Split into simpler sentences: Will stated that Barr could have a similar effect on the election as Ralph Nader in 2000. He described the potential effect as a "punishment" for presumptive Republican Party nominee John McCain for his co-sponsorship of the Bipartisan Campaign Reform Act of 2002, which Barr opposed.