WHAT'S OPEN?: Here's how the shutdown is affecting key parts of the federal government

Thousands of federal employees began their weekends gripped with doubt, uncertain of when they'll be able to return to work and how long they'll have to go without being paid after a bitter political dispute in Washington triggered a government shutdown.

And now that the shutdown has extended into the work week, federal employees entered Monday unsure of when their next paycheck would come.

Many government operations will continue - US troops will stay at their posts and mail will get delivered. But almost half the 2 million civilian federal workers will be barred from doing their jobs.

The longer the shutdown continues, the more likely its impact will be felt. Sen. John McCain, R-Arizona, said Republicans and Democrats share the blame.

"Political gamesmanship, an unwillingness to compromise, and a lack of resolve on both sides have led us to this point," McCain said in a statement Saturday.

How key parts of the federal government would be affected by a shutdown: