The Obama administration today will defend a requirement thatAmericans obtain insurance or pay a penalty — the core of thepresident's health care overhaul — in a Supreme Court case centralto the Republican campaign to take over the White House.

A group of 26 states will say that Congress exceeded itsauthority in approving the mandate, as the justices hear theirsecond of three days of arguments. The government, defending thepresident's signature legislative victory, will contend thatCongress can require people to buy insurance under itsconstitutional power to regulate the interstate health-caremarket.

During yesterday's opening session, several justices suggestedthey will reject an argument that they can't consider the caseuntil the penalty is imposed in 2015.