WHY IT MATTERS: The environment
Everyone wants clean air and water. But people also want to drive their cars whenever they wish and light up a room by flipping a switch. It's a never-ending balancing act for government as it tries to protect health and the environment while promoting economic growth and jobs.
Where they stand:
President Barack Obama achieved historic increases in fuel-economy standards that would save drivers money at the pump while raising the cost of new vehicles. The administration also imposed the first-ever regulations on heat-trapping gases blamed for global warming and tightened standards on toxic mercury pollution from power plants. It also set new standards lowering the amount of soot that can be released into the air.
Obama failed to persuade a Democratic Congress to pass limits he promised on carbon emissions and shelved a plan to toughen health standards on lung-damaging smog.
Republican Mitt Romney has expressed doubts about the cause of climate change and criticized Obama's treatment of coal-fired power plants as punitive. He opposes treating carbon dioxide as a pollutant and wants to amend clean water and air laws to ensure the cost of complying with regulations is balanced against environmental benefits.
Why it matters:
Federal rule-makers always face a tension between protecting people from getting sick or injured while preserving jobs and keeping government power in check. The Obama administration has been accused by Romney and other Republicans of tilting too far in favor of regulation.
The Environmental Protection Agency in particular has come under sharp criticism for issuing the first-ever regulations aimed at reducing gases blamed for global warming and for a separate rule cracking down on mercury pollution from power plants.
The greenhouse gas rules will reduce emissions of carbon dioxide and other heat-trapping gases from factories and power plants, as well as from automobile tailpipes. The power plant rule controls mostly older, coal-fired plants.
The EPA says it had no choice but to act after concluding that carbon dioxide and other pollutants endanger human health and welfare. Power plants are the largest source of manmade mercury in the environment. Mercury is a toxic metal that's known to impair brain development in children, including those exposed in the womb.
The new rule will have a major impact on coal, which accounts for about 40 percent of U.S. electricity production. Dozens of coal-fired plants across the country could be forced to shut or spend billions on plant upgrades.
Changing economics, including low natural gas prices and reduced electricity demand, are also major factors in coal-plant retirements. Most of the plants likely to close are decades old and inefficient.
Obama maintains he has focused on common-sense rules. In January 2011, he ordered federal agencies to get rid of rules that were overly burdensome, redundant or inconsistent. The ax fell on hundreds of regulations.
One high-profile reversal was on a pledge to strengthen restrictions on lung-damaging smog. Obama had promised to impose a standard that was stricter than one left in place by former President George W. Bush. But after months of review, the White House halted the new smog standards, explaining it was acting to reduce regulatory burdens and uncertainty in a shaky economy.
Many of the delayed rules could take effect in a second Obama term. Romney is likely to try to relax or scrap them.