The US president's Supreme Court nominee, Samuel Alito, has faced tough questions about his views from senators gauging his suitability for the post.
Some view the hearings as a battle for the legal soul of the nation
On the key issue of abortion, Mr Alito told a panel he would approach any case at the court "with an open mind".
He said judges must heed precedent and that no-one was above the law.
If approved Mr Alito, a conservative, will replace Sandra Day O'Connor, who has often held the swing vote on abortion and other contentious issues.
Mr Bush's earlier choice for the post, lawyer Harriet Miers, withdrew when conservatives refused to support her.
'No blank cheque'
Supreme Court justices have vast power and are appointed until they die, resign or are impeached.
The 18-member Senate Judiciary Committee's examination of Mr Alito - expected to last at least two days - began the first full days of questions from Chairman Arlen Specter about abortion and domestic spying.
Mr Alito, 55, a government lawyer under the Reagan administration in the 1980s, said his writings then opposing abortion reflected an attorney representing a client's interest.
He had once written that he did not believe the constitution protected the right of women to abortion.
He also defended his 1991 judicial vote in which he said a law requiring women seeking abortions to notify their husbands was permissible under the constitution, AP news agency said.
On the issue of presidential powers, he said he agreed with a statement by Justice O'Connor that a state of war "is not a blank cheque for the president when it comes to the rights of the nation's citizens".
"Our constitution applies in times of peace and in times of war, and it protects the rights of Americans under all circumstances," he said.
"The president has to follow the constitution and the law is in fact one of the most solemn responsibilities of the president and it's set out expressly in the constitution is that the president is to take care that the laws are faithfully executed," he said.
President Bush has praised Samuel Alito's judicial experience
The Republicans hold a 55 to 45 seat majority in the 100-seat Senate, which must approve Mr Alito.
Conservative Republicans and anti-abortion campaigners have welcomed his nomination.
But Democrats fear Mr Alito could swing the court too far to the right and have threatened to block his nomination, amid concerns he will use his position on the court to overturn long-standing civil rights.