In every election-changing close vote on legislation that passes in the U.S. House, there are two or three U.S. House Members who switch their vote at the last minute.
Usually, these are newbie House members, freshmen or sophomores who succumb to pressures of their leadership, but forget their own districts and what they need to do to keep their jobs.
Thus, we are reminded of the case of Marjorie Margolies-Mezvinsky (D-PA) who famously switched her vote to give then President Clinton his tax increase.
It was her vote that passed the bill.
The vote by Marjorie Margolies-Mezvinsky (D-PA) was an expensive one: she lost the following year.
“After defeating Republican Jon D. Fox  in a close contest, she became a member of the 103rd Congress . However, she was not re-elected. Losing in 1994 to her 1992 opponent, she was one of 34 Democratic incumbents who were defeated in the Republican Revolution . Her defeat was blamed on her vote for President Bill Clinton ‘s controversial 1993 budget, for which she was the deciding vote. After the vote, Rep. Robert Walker  (R-Pennsylvania) reportedly mocked her, jumping up and down and said “Goodbye, Marjorie” alluding to the fact that her deciding vote would cost her the seat.”
You can bet that any Democratic House member(s) who switches their vote to give Speaker Pelosi her health care victory will be targetted en masse, by the legions who are strongly opposed.
It will cost any last-minute-Democratic-House-vote-switching-member their seat. Of course, if the bill fails then there will be no Margolies-Mezvinsky Effect.
For those House Members who think they may collapse under leadership pressure, here is a tried and true method for avoiding that fate: hide. Vote and get off the House floor, turn off your cell phone and hide somewhere you can not be found. Not one of your usual haunts. And go alone, so you aren’t outed by your staff.