WASHINGTON — Caught between nervous Democrats and emboldened Republicans, President Barack Obama on Friday stepped up the sales pitch on his health care overhaul as the final elements of his top domestic achievement go into effect. With his legacy and the law's success at stake, Obama said: "The law is here to stay."

Behind the scenes, the White House readied a campaign-style effort to get healthy young people to sign up for the insurance "exchanges" in order to keep premium costs from skyrocketing. On Capitol Hill, House Republicans are planning yet another vote to try to try to repeal the law.

The insurance exchanges are the centerpiece of the landmark overhaul of the nation's health insurance system and the White House mobilization is crucial to the success of the health care law and, by extension, to Obama's place in history as the first president in decades to expand health care coverage.