This was ostensibly a vote on a motion to table (kill) a "motion to commit" (i.e. an amendment) by Sen. Jim DeMint (R-SC) that would have allowed individuals to purchase health insurance plans across state lines. (If passed, a motion to commit sends the legislation back to committee with instructions to amend the legislation as specified.) The measure DeMint sought to amend was a “companion bill” making a number of changes to health care reform legislation already signed into law by President Obama. The underlying context was that Republicans were trying to attach amendments to the companion bill in order to send it back the House, where it had passed by a narrow margin. CNN reported that Republicans had chosen to offer a slew of amendments in order to “undermine the measure,” while the Associated Press characterized the amendments as “a final drive to thwart President Barack Obama's health care remake.”
 
DeMint urged support for his amendment: “…This motion will ensure that the new government health regime that has just been made law will not prohibit Americans from purchasing private health insurance plans across state lines without going through a government exchange.”

Sen. Max Baucus (D-MT) argued that purchasing of health plans across state lines was only feasible if those plans were part of the exchanges, where they would be regulated. (Under the health care reform legislation already signed into law by President Obama, individuals who do not receive health insurance from their employers can purchase insurance from state “exchanges.” In the exchanges, individuals can choose from a variety of private plans.) Baucus made a motion to table (kill) DeMint’s motion to commit, saying: “Allowing them  [insurance companies] to sell across State lines is in concept a good idea, but it must be done responsibly.…Once the exchange is open in 2014, insurance companies will automatically be able to sell across state lines. But to allow sales now would be irresponsible…”

After the House and Senate both passed their respective health care reform bills, the two chambers had intended to reconcile those two bills into a final package. After the House and Senate passed that final package, it would have been sent to President Obama, who would have signed it into law. Sen. Scott Brown (R-MA), however, won a special election to replace the late Sen. Ted Kennedy (D-MA) before the final health care bill could be brought up for a vote. Brown's victory gave Republicans 41 votes in the Senate, leaving Democrats with 59 members – one vote short of the 60 votes they needed to defeat a unanimous Republican filibuster against the final health care bill. 

In order to pass comprehensive health care legislation without a 60-vote majority in the Senate, Democratic leaders devised a plan in which the House would pass the Senate health care bill (H.R. 3590), thereby enabling the president to sign it into law. The House would then pass a separate companion bill (H.R. 4872) to make changes to the Senate health measure under a process known as "budget reconciliation." Bills considered under budget reconciliation cannot be filibustered under Senate rules. This process allowed the House to make changes to Senate-passed health care legislation without sending the entire health bill back to the Senate, where it could have been filibustered indefinitely.   The companion bill incorporated changes to the Senate health care legislation desired by House Democrats. The House passed the companion measure, and sent it to the Senate, where Democratic leaders hoped to defeat all amendments -- thereby avoiding a second vote in the House on a substantively changed bill; a vote that Democrats might have lost given the already tight margin when it was voted on the previous week.

The Senate voted to table (kill) DeMint’s motion to commit by a vote of 56-43. 56 Democrats voted “yea.” All 40 Republicans present and 3 Democrats voted “nay.” As a result, the Senate rejected an amendment Democratic leaders feared could have torpedoed the entire companion health care bill and would have allowed individuals to purchase health insurance plans across state lines.