WASHINGTON — Slowly but steadily, support is building behind President Barack Obama’s health care legislation in the House, with the intense lobbying and politically targeted changes to the bill winning over an Ohio Democrat today.

Obama himself was talking up the sweeping overhaul in a midday speech today in Virginia, his fourth outside-the-Beltway event in two weeks as he scrambles to rally the public ahead of a climactic vote this weekend. On Capitol Hill, congressional leaders were focusing on those rank-and-file Democrats, including moderates and opponents of abortion, who remained undecided after the release Thursday of a final package of changes to the massive 10-year, $940 billion legislation.

Rep. John Boccieri, D-Ohio, announced at a Capitol Hill news conference that he would switch his vote to “yes.” The freshman lawmaker said he was “standing up today and doing what I believe in.”

Labor unions and other pro-reform groups ran ads in his district urging him to back the measure.

In his speech today, Obama described the stakes of this weekend’s health care vote in stark terms, using words uttered so rarely out of the White House that they seem all but banned: “If this vote fails.”

With Sunday’s expected vote hanging on the support of just a handful of wavering Democrats, Obama delivered a closing argument for the goal to which he has devoted much of his presidency and on which its future could pivot. Before a large, raucous rally at suburban Virginia college, the president summoned both pragmatism and principle to sway the undecideds to his side.

He emphasized the bill’s provisions that would go into effect this year, including those banning insurers from denying coverage to those with pre-existing conditions, dropping coverage when a person becomes ill or imposing annual or lifetime limits on care, requiring free preventive care and allowing children to stay on parents’ policies into their 20s. He said “the insurance industry will continue to run amok” if the vote fails.

Obama urged lawmakers to reach beyond today’s disputes and grasp the history-making aspect of the effort.

“It’s a debate that is not only about the cost of our health care but the character of our country, about whether we can still meet the challenges of our time, about whether we’re still a nation that gives its citizens a chance to reach their dreams,” Obama said.

Pointing to contentious debates decades ago over creating the now-popular Social Security and Medicare programs, he said that “when we have faced such decisions in our past, this nation has chosen time and again to extend its promise to more of its people.”

“I know this will be a tough vote. I know that Washington has treated this debate like a sport,” he said.

The White House and Democratic leaders trumpeted two new converts to their cause, as retiring Rep. Bart Gordon, D-Tenn., and first-term Rep. Betsy Markey, D-Colo., announced their support after opposing an earlier version of the legislation last year. Markey cited improved deficit cuts. Gordon said his backing was unrelated to a new provision sending higher Medicaid payments to Tennessee hospitals that treat large numbers of uninsured.

The conversation was all about how Democrats would vote since Republicans have formed a virtually impenetrable phalanx of opposition for the past several months.

As rumors flew around the House chamber of more possible opponents-turned-supporters – and also of previous “yes” voters who might withdraw their support – Pelosi worked her members, seeking out lawmakers individually or in small groups on the House floor to try to win them over. With Republicans unanimously opposed after a year of corrosive debate, the vote set for Sunday was expected to be a cliffhanger, and Democratic leaders don’t yet command the 216 commitments they need.

Obama postponed until June a planned Asia trip that was set to begin Sunday, allowing him to stay in town for the House vote and action next week in the Senate.

House Democrats were hoping to get a letter of support today signed by enough Senate Democrats to guarantee passage of the package of changes in that chamber, something leaders hope will reassure rank-and-file House members that they won’t be left hanging out to dry.

But a climate of uncertainty remained the dominant dynamic as the vote drew near. House Majority Leader Steny Hoyer acknowledged today that the leadership still lacks enough votes to win this weekend’s climactic vote.

The Maryland Democrat said on CBS’s “The Early Show” he believes House members “are going to conclude by Sunday that this is a bill that does what we said it was going to do.”

And Rep. Bart Stupak, a Michigan Democrat who has led a dozen House Democrats in opposing the bill because of the abortion issue, reiterated Friday that his group may vote no when the final vote comes.

“My group of 12 here can make the difference on this vote,” he said on ABC’s “Good Morning America.”

Stupak said “there’s a principle we’re standing up for. … Protect the sanctity of life. Keep current law. No public funding for abortion. Let’s keep that principle intact and you can probably get our vote.”

With the addition of the 153 pages of revisions, the bill would expand health care to 32 million uninsured, bar the insurance industry from denying coverage on the basis of pre-existing medical conditions and trim federal deficits by an estimated $138 billion over the next decade.

Beginning in 2014, most Americans would be required for the first time to purchase insurance or face penalties if they refused. Large businesses would face fines if they did not offer good-quality coverage to their workers. Millions of families with incomes up to $88,000 a year would receive government help to defray their costs.

To address concerns of House Democrats, those subsidies were raised by an estimated $25 billion over a decade in the package of changes offered Thursday. Seniors who experience a gap in coverage in the Medicare prescription drug program would receive a $250 rebate this year – an election-year bragging point for Democrats as they look toward the fall campaign with control of Congress at stake. A special deal giving extra Medicaid money to Nebraska was struck in exchange for more Medicaid money for all states, though other special deals decried by Obama stayed in the bill.

The changes also included another of Obama’s top priorities: Federally guaranteed student loans would now be made only by the government, ending a role for banks and other for-profit lenders who charge fees. The savings, an estimated $60 billion over a decade, would increase Pell grants for needy college students as well as support for programs such as aid to historically black colleges, a priority of the Congressional Black Caucus.

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