Monday begins a pivotal week in Congress, the last opportunity this year to pass some kind of economic stimulus package to boost the ailing economy. This will also be a decisive moment for legislation to keep the federal government running on a leaner budget for the rest of the fiscal year.

Even though House and Senate leaders agree that the economy needs help, the two sides have failed to agree on how to approve an extension of the payroll tax holiday that President Obama pushed as part of his jobs-creation package in September. Set to expire on New Year’s Day, the tax provision has emerged as a key stumbling block in the annual rush to approve must-have legislation before Congress adjourns for the year.