The health-insurance marketplaces at the center of President Barack Obama's health law saw a surge of consumer interest Tuesday that surprised even many of the law's backers. But the debut proved patchy, with few applicants actually able to buy coverage on clogged websites that were bedeviled with technological problems.

Federal officials said more than 2.8 million visitors between midnight and late afternoon contributed to long wait times for access to healthcare.gov, the website they are running for 36 states.

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