Earlier this afternoon, Democrats broke Senate rules in order to defeat the Kyl amendment, which would have set the top death tax rate at 35 percent with a $5 million exemption. Under current law, the death tax will jump from zero in 2010 to a top rate of 55 percent with a $1 million exemption in 2011.

You can watch the Democrats' shenanigans unfold here. About four minutes after the vote was scheduled to end, the measure was winning 50 to 48, and Sen. Tester announced: "Time has expired. The clerk will tally the vote."

Then senators Dodd and Biden come in to defeat the measure 50 to 50--Cheney was not in the Senate to break the tie.

A GOP aide told me that Republicans may ask Cheney to come to the Senate tonight if they can bring the amendment up for another vote. But the aide doubted the measure would pass because Mary Landrieu--a Louisiana Democrat up for reelection this year--changed her vote from "nay" to "yea" only after learning that Dodd and Biden were on their way to defeat the bill.

Yet even if the amendment didn't pass, Cheney's presence could force Landrieu to officially flip-flop on the same vote on the same day.