Washington ? As demonstrations swirled outside, Supreme Court justices signaled on Monday they are ready to confront without delay the keep-or-kill questions at the heart of challenges to President Barack Obama’s historic health care overhaul. Virtually every American will be affected by the outcome, due this summer in the heat of the election campaign.

On the first of three days of arguments — the longest in decades — none of the justices appeared to embrace the contention that it was too soon for a decision.

Outside the packed courtroom, marching and singing demonstrators on both sides — including doctors in white coats, Republican presidential candidate Rick Santorum and even a brass quartet — voiced their eagerness for the court to either uphold or throw out the largest expansion in the nation’s social safety net since Medicare was enacted in 1965.

Today’s arguments will focus on the heart of the case, the provision that aims to extend medical insurance to 30 million more Americans by requiring everyone to carry insurance or pay a penalty.

A decision is expected by late June as Obama fights for re-election. All of his Republican challengers oppose the law and promise its repeal if the high court hasn’t struck it down in the meantime.

On Monday, the justices took on the question of whether an obscure tax law could derail the case.

The 19th-century law bars tax disputes from being heard in the courts before the taxes have been paid.

Under the new health care law, Americans who don’t purchase health insurance would have to report that omission on their tax returns for 2014 and would pay a penalty along with federal income tax on returns due by April 2015. Among the issues facing the court is whether that penalty is a tax.

Solicitor General Donald Verrilli Jr., defending the health law, urged the court to focus on what he called “the issues of great moment” at the heart of the case. The 26 states and a small business group challenging the law also want the court to go ahead and decide on its constitutionality without delay.

But one lower court that heard the case, the federal appeals court in Richmond, Va., has said the challenge is premature. No justice seemed likely to buy that argument Monday.

The justices fired two dozen questions in less than a half hour at Washington attorney Robert Long, who was defending the appeals court ruling.

Verrilli said Monday’s argument dealt with the meaning of the word in the context of the 19th century-law, the Anti-Injunction Act. Today’s session will explore Congress’ power to impose the insurance requirement and penalty. In that setting, he said, Congress has the authority under the Constitution “to lay and collect taxes,” including the penalty for not having insurance.