At 81, Anthony Kennedy is the second-oldest justice on the United States Supreme Court, and many people expect him to retire next year.

But at the moment, he just might be the most powerful political figure in the United States.

Justice Kennedy is widely expected to cast the deciding vote in a case that could dramatically reduce the Republican Party's advantage in Michigan and two dozen other states where the GOP controls the process of drawing legislative and congressional boundaries.

►More Dickerson: Why the future of Michigan politics may depend on the Supreme Court's gerrymandering case

Gerrymandering is defined as the process of drawing legislative boundaries in a way designed to magnify the impact of one party's voters while diminishing its opponent's -- is as old as representative democracy. But technological advances that make it possible to predict voter behavior with greater accuracy and precision allowed Republicans who controlled the redistricting process in most states after the 2010 Census an unprecedented advantage.

Did GOP go too far?

In oral arguments set for Tuesday morning, the plaintiffs in Gill v. Whitford will argue that Wisconsin Republicans violated the constitutional rights of that state's Democratic voters in 2011 when they adopted new political boundaries that assured the GOP control of the state legislature even when Democratic legislative candidates won the most votes.

A federal district court panel in Wisconsin agreed with the plaintiffs last year, adopting a mathematical test it said proved Republicans had systematically diluted the impact of Democratic voters. Michigan is among the states that could be forced to withdraw their own maps if Supreme Court justices agree that the "efficiency gap" identified by the lower court gives Wisconsin's Republicans an unconstitutional advantage to translate their votes into legislative representation.

The court's four most liberal justices seem poised to uphold the lower court ruling; conservatives led by Chief Justice John Roberts have suggested that legislators, not the courts, should decide when gerrymandering has gone to far.

When unfair becomes unconstitutional

Kennedy, who cast the deciding vote in the high court's landmark ruling striking down state bans on same-sex marriage, has sided with conservatives up to now. But he has written in previous gerrymandering cases that the court might be obligated to strike down some gerrymandered districts if challengers could show that they violated the constitutional rights of one party's voters.

Justices will probably rule in the Wisconsin case sometime next year. If the plaintiffs prevail, Michigan would likely be forced to level its own political playing field no later than the legislative and congressional elections in 2020.

That gives Kennedy an outsized role in determining what the political landscape will look like, here and dozens of other states, in the decade ahead.

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