Both the Democrat  and Republican payroll tax cut plans were defeated in the Senate tonight.

The Democrats’ proposal was defeated by a vote of 51-49. One lone Republican, Sen. Susan Collins of Maine, voted with the Democrats.

Immediately after,   the Republican plan went down too, by a vote of 20-78, with Sens. John McCain of Arizona and John Kerry of Massachusetts abstaining.

Each plan needed 60 votes in the Senate to move ahead, and both fell far short of that threshold.

While the defeat of both plans came as no surprise, more than half of the Senate Republican conference defected on its own bill. Democrats will almost surely jump on this statistic for political gain in the days ahead, as Senate Majority Leader Harry Reid’s statement suggested this evening.

“Republicans spent this week trying to convince us that they support middle-class tax cuts, but tonight a majority of Senate Republicans voted against their own bill – calling into question whether they support middle-class tax cuts at all,” Reid said. “I hope Republicans will decide that the economic security of hard-working Americans is more important than protecting the wealthiest 1 percent.”

One Republican, Sen. Mark Kirk of Illinois, and one Democrat, Sen. Joe Manchin of West Virginia argued earlier today that they would not vote for either the Democratic or the Republican version of the bill because both would harm Social Security.

“I would actually say even the political vote is to vote against this so that you’re for Social Security,”  Manchin said on the Senate floor this afternoon.

With the defeat of both bills, aides say both parties will sit down and start  to hammer out a compromise. Both sides say that the Senate will not go home for Christmas without passing a payroll tax cut extension for next year. The disagreement is over how to get there and pay for it.

The Senate has adjourned  until 2 p.m.  Monday.