The Senate Democratic Party leadership. (Melina Mara/WashingtonPost)

House Republicans are planning to raise country's borrowing limit for three months, with a promise to raise it again if Senate Democrats pass a budget. Sen. Chuck Schumer (D-N.Y.) promised Sunday that it would happen. If it does, it would be the first time since 2009 that Senate Democrats have passed a budget.

Why is that?  Here's a (relatively) simple explanation.