The Senate vote, 27-7, would be enough to override a gubernatorial veto. But the House tally, 96-55, would fall 13 votes short, even including the nine members who were absent for the vote.
A veto would give renewed hope to Rep. Russ Carnahan, D-St. Louis, who would lose his congressional district under the map approved by the Legislature. At the state Capitol on Wednesday, he emphasized that his camp is looking to a long road yet ahead.
"We're going to stay firm on getting to a map that respects the key regions of the state and especially that respects the St. Louis region in a way that doesn't slice and dice districts," Carnahan said in an interview.
The map could be redrawn if it faces a legal challenge. Wednesday, House Speaker Steve Tilley, R-Perryville, voiced confidence in the map's constitutionality.
"I do believe it will withstand legal challenge, and I'm going to encourage the governor next time I visit with him that he should look at the map and look how it's drawn, and encourage him to sign it," Tilley said.
The "Grand Compromise" map, as some legislators have termed it, moves the 2nd District north from its position on the original House map. The district would include more of St. Charles County and less of Jefferson County than the House originally wanted.
That could make for a more competitive 2nd District, currently the only new congressional district in which the incumbent member of Congress might not seek re-election.
Many observers expect Rep. Todd Akin (R) to jump into the 2012 race against Sen. Claire McCaskill (D). That would leave an open seat in the state's 2nd district, which former state Republican Party Chairwoman Ann Wagner is already exploring a run for.
A move by Akin could also clear the way for Carnahan, who could run against Wagner in an open-seat contest.