By Dianne Feinstein

Originally appeared in the San Francisco Chronicle

The vacancy on the U.S. Supreme Court will resonate for years to come, particularly if Republicans fail to do their job by blocking a nominee well into 2017.

The Supreme Court is the final arbiter on federal legal questions. When lower courts reach different conclusions on important federal issues — a frequent occurrence — the Supreme Court resolves those disputes. The court’s rulings also establish precedent, guiding judges in future cases.

But with just eight judges, the court could deadlock on important cases. These 4-4 ties would perpetuate uncertainty in the law, with important legal questions going unanswered. In case after case, this could harm businesses and individuals alike — all because the Senate did not do its job.

The Senate has a constitutional obligation to consider the president’s nominee to the court and prevent the potential harm of tie decisions. A deadlocked court means appellate court rulings — often in major cases — remain in place, which would mean the law would vary throughout the land. At least one of the two sides of a case would be denied a Supreme Court ruling.

Justices themselves have said how important it is to avoid a deadlocked court. Justice Antonin Scalia, when he decided not to recuse himself in a case involving then-Vice President Dick Cheney in 2004, noted that the court would be “unable to resolve the significant legal issue presented by the case.”

Justice William Rehnquist warned in 1972 that that a divided court “would lay down one rule in Athens, and another rule in Rome.”

In 2010, Justice Elena Kagan recused herself from Flores-Villar vs. United States. This case was going to decide whether a U.S. citizen father needed to reside in the United States longer than a U.S. citizen mother in order to confer citizenship to his child born abroad.

Because the court was deadlocked and voted 4-4, a child in one part of the United States may be considered a citizen while another in the same situation in a different judicial circuit may not be a citizen. This issue remains unresolved.

In 2007, Chief Justice John Roberts recused himself from Warner-Lambert vs. Kent, a case to decide whether individuals can sue for injuries caused by defective pharmaceuticals when the drugmaker allegedly hid information from federal regulators. The deadlock in that case failed to clarify the law, which now varies across the country. Plaintiffs in the Sixth Circuit are now unable to sue for personal injury in this situation, while individuals harmed in the same way by the same drug in states covered by the Second Circuit are.

In 1987, in the days before Justice Anthony Kennedy took his seat, the court heard U.S. vs. Carpenter & Winans. The case, which came before the stock market crashed that year, involved defendants who had been convicted of securities fraud based on allegations that they misused information from a prominent investment advice column in the Wall Street Journal.

The Supreme Court could not determine whether that action could be a basis for prosecution. The law was left unclear for 10 years, during which time some lower courts overturned criminal convictions for this sort of fraud.

These are just a handful of examples of what could happen in every case a divided Supreme Court hears.

With important issues on the horizon for the court that will affect Americans across the country, we must have a full slate of justices as soon as possible to hear and resolve those cases. The Senate must do its job and give the president’s nominee full and fair consideration.

Dianne Feinstein represents California in the U.S. Senate.