Proportional representation would clearly be good for third parties -- for the first time they would have a realistic chance to elect their candidates to office. But does that mean that it would be bad for the major parties? It might appear so. For example, voters would have more choices with PR and some would probably defect from the major parties to join alternative parties. However, if we look carefully at the likely impact of PR, it turns out that its effects on the major parties are not nearly as bad as they first appear. In fact, PR would actually have several advantages for our traditional parties.
Proportional representation would certainly help many Republican and Democratic voters — primarily by assuring them of representation. No such assurances exist now. In every national election, tens of millions of major party supporters come away from the polls with no one to represent them in Congress. Republicans living in a predominately Democratic districts stand little chance of electing their candidate — and vice versa. Even if the smaller of the two parties manages to marshal 30%-40% of the vote, those votes would usually be wasted on a candidate that loses. This frustrating situation is all too common. In fact, almost all of the wasted votes in the United States are cast by supporters of the two major parties — not third party supporters.
In addition, these wasted votes often produce unfair election results, where one party wins far fewer seats than it deserves. For example, in the 1994 elections for the U.S. House of Representatives, the Democrats won 42 percent of votes in Iowa, but none of the state's five seats in the House. A similar fate befell the Republicans in an early 90s election in Massachusetts, where they won 35% of the vote in the contested districts, but won no seats in the eleven person House delegation.
The only way to be sure of stopping this kind of political travesty is to adopt proportional representation. In this system, even if a major party has only 20%-30% of the voters in a district, they will still be able to win 20%-30% of the seats. In the Iowa example, the Democrats' 42% of the vote would have won them two of the five congressional seats under PR rules, rather than none. Only proportional representation ensures that both major parties will win their rightful share of seats.
Of course, this still leaves the problem of Democratic and Republican parties losing some members to the third parties. There is a good chance, for instance, that ultra-liberal Democrats might break away from the main party to form their own leftist party. And the Republicans might lose some of their more conservative members to a far right party. But would this be a disaster for the two major parties? Probably not. The number of defecting voters would probably be small. The Republicans and Democrats would still reign as the two largest parties.
In addition, the "loss" of these splinter groups would, in a sense, only be temporary. These minor parties would most likely join up again with the main party in a legislative coalition. Say, for example, that a Christian Coalition party broke off from the Republican party. In the legislature, these parties would be natural allies on many issues and would join together their conservative forces in most legislative battles with the left.
Losing some voters to splinter parties would also have at least one positive impact on the two major parties. The exodus of the more radical members of these parties would significantly cut down on fractious internal conflicts. The Democratic party, for instance, is often racked by intense and divisive debates between its centrist and leftist elements. When the leftist groups lose these fights, they feel resentful and may offer little active support for the party's nominees. But when the party adopts the positions of these fringe groups, the mainstream of the party feels betrayed. And as we saw in the case of George McGovern in 1972, the victory of fringe groups in a party can drive away many traditional supporters. Losing some of these more radical voters to other parties would allow the major parties to become more moderate, unified, and cohesive.
So we shouldn't be too quick to conclude that PR would be all bad for the major parties. The ill effects of proportional representation on these parties are often greatly exaggerated, and it is clear that some consequences of PR will actually be beneficial to the Republicans and Democrats.