Here's how this all started.

In May, the Senate approved its version of what's called the supplemental spending bill. The legislation primarily was used to fund the wars in Iraq and Afghanistan, along with a few extras.

The Senate sent the bill to the House.

Then...

The when the House took up the measure, the Democratic leadership engineered a number of votes and efforts to either withdraw troops, de-fund the conflict or impose timetables on pulling out. None of those amendments passed. But..the House did add on at that time more than $20 billion for jobs and aid to states so they wouldn't have to lay off teachers.

At that point, the House and Senate have passed different bills. So the House kicked it back to the Senate. Where essentially the Senate ignored the House changes and punted it back to the House.

So...late last week, the House approved the Senate's version of the bill, thus funding the wars and imposing no conditions on the conflict.

Meantime, today the Senate invoked cloture on the jobs and teachers bill. That means the Democrats broke a Republican filibuster, poising the Senate to approve the measure tomorrow.

So, in order for lawmakers to send to President Obama actual legislation to sign, the House must adopt what the Senate is prepared to adopt tomorrow. Both the House and Senate must be in synch on the measures they pass before they can send a bill to the White House for the president's signature.

That's why the House must return to session next week.

There is precedent for this happening in the middle of lengthy recesses. Former House Majority Leader Tom DeLay, R-Texas, brought the House back on Palm Sunday in 2005 to vote to rebuff the decision of a Florida judge who allowed the feeding tube of Terri Schiavo to be removed. Schiavo had been in a vegetative state for years.

Later that summer, Congress came back during the August recess to approve emergency money for FEMA after Hurricane Katrina devastated the Gulf Coast.