And then there were three: Today's big Supreme Court rulings

WASHINGTON — The Supreme Court last week handed down decisions in the most closely watched cases of the term: same-sex marriage and Obamacare.

But it's not over yet: On the final day for decisions Monday, the justices will weigh in on three important cases involving fair elections, clean air and capital punishment.

Here's a rundown (and you can also use our Supreme Court Tracker to catch up with all the big decisions from this term).

• Clean air. Environmental regulations approved by the Obama administration regularly come before the Supreme Court, and this year is no exception. A major rule requiring coal- and oil-fired power plants to reduce emissions of mercury and other toxic air pollutants hangs in the balance.

The justices appeared closely divided on the central issue in the case when it was argued — whether the Environmental Protection Agency should have considered the nearly $10 billion annual cost in relation to the potential benefits before approving the regulation. A decision in favor of objecting states and utilities could send the EPA back to the drawing board.

Prep for the polls: See who is running for president and compare where they stand on key issues in our Voter Guide

• Lethal injections. The death penalty also is never far from the high court's docket. After a steady diet of cases and emergency appeals on issues such as claimed intellectual disabilities and the actions of defense lawyers and prosecutors, the court now must rule on a relatively new method of execution.

The case involves the use of a sedative called midazolam as part of a three-drug cocktail used by several states, including Oklahoma, where three death-row inmates are challenging its use. Unlike stronger barbiturates that are in short supply, the drug has failed in some cases to block pain and suffering during the lethal injection process.

• Political maps. In the second case to reach the court this year on political redistricting, the justices must decide whether nonpartisan commissions can replace state legislatures in drawing congressional district maps every 10 years.

Those commissions are used in seven states, including California, to take the redistricting process out of the hands of politicians with a vested interest. But the Arizona state Legislature's Republican majority argued that the Constitution gives that power solely to state legislatures. A majority of the court's justices appeared to agree during oral arguments.