(CNN) -- Sen. Barack Obama received key endorsements Friday from a top former Clinton administration official and two former Democratic senators.
Robert Reich, a former Labor Secretary under President Clinton, endorsed Sen. Obama Friday.
Robert Reich, a former Clinton cabinet member and longtime friend of the former president, formally endorsed Obama's White House bid, saying that "my conscience won't let me be silent any longer."
"Although Hillary Clinton has offered solid and sensible policy proposals, Obama's strike me as even more so," Reich wrote on his blog.
He served as the Secretary of Labor from 1993-1997 and is currently a professor at Brandeis University.
"His plans for reforming Social Security and health care have a better chance of succeeding," Reich continued. "His approaches to the housing crisis and the failures of our financial markets are sounder than hers ... He has put forward the more enlightened foreign policy and the more thoughtful plan for controlling global warming."
Reich, whose relationship with the Clintons dates back to their law school days at Yale, has long been a critic of the New York senator's White House bid. Shortly before the Iowa caucuses in January, he wrote that voters would have a choice "between someone who talks the talk, and somebody who's walked the walk."
"I don't get it," he wrote then. "If there's anyone in the race whose history shows unique courage and character, it's Barack Obama. HRC's [Hillary Rodham Clinton's] campaign, by contrast, is singularly lacking in conviction about anything."
Reich also criticized Bill Clinton earlier in the year over the former president's sharp attacks on Obama in South Carolina.
"Bill Clinton's ill-tempered and ill-founded attacks on Barack Obama are doing no credit to the former president, his legacy, or his wife's campaign," he wrote in January. "Nor are they helping the Democratic Party."
Asked to respond to Reich's endorsement, Clinton spokesman Mo Eleithee said, "Didn't he endorse him last year?"
Reich is the latest former Clinton administration official to announce his support for Obama. Last month, New Mexico Gov. Bill Richardson, who held several positions under Bill Clinton, also came out in support of the Illinois senator. Clinton supporter and CNN political analyst James Carville later called that an "act of betrayal."
Meanwhile, the Obama campaign announced that former Sens. Sam Nunn of Georgia and David Boren of Oklahoma endorsed the Illinois senator, and agreed to serve on the campaign's national security policy team.
Nunn served 25 years in the Senate and was chairman of the Senate Armed Services Committee from 1987 to 1995. He said Obama is "our best choice to lead the nation."
"I believe that he will bring to the White House, high principles, clear vision and sound judgment," he added.
Boren -- who served in the Senate from 1979 to 1994 and is the longest-serving Chairman of the Senate Select Committee on Intelligence -- was one of Bill Clinton's top choices to replace Les Aspes in 1994 as U.S. Secretary of Defense.
He said Obama is a person of "sound and good judgement."
Obama responded to the endorsements in a statement, saying the two "will be important sources of advice and counsel for our campaign in the months ahead." Watch more from the campaign trail »
The endorsements come just four days before Pennsylvania's April 22 primary. At stake: 158 delegates.
Also on Friday, Clinton accused Obama of "complaining" about Wednesday night's debate in Pennsylvania and hinted her rival might not be equipped to handle the rigors of the Oval Office. Watch more from Wednesday's debate »
Obama said Thursday that Clinton was "in her element" at the debate, telling a North Carolina crowd she "took every opportunity to get a dig in."
"That's her right to kind of twist the knife in a little bit," he said, before adding that he understands why she's using what he calls the tactics of the GOP. Watch more of Obama's comments »
Clinton told an interviewer Friday morning on WTXF in Philadelphia that "being asked tough questions in a debate is nothing like the pressures you face inside the White House."
"When the going gets tough you can't run away," she said of Obama.
Meanwhile, Obama faced more criticism Friday -- this time from Sen. John McCain.
McCain's campaign is crying foul over what it characterizes as repeated distortions from Obama.
The most recent dustup comes after Obama criticized McCain earlier Friday for comments the Arizona senator made in an interview on Bloomberg Television.
"John McCain went on television and said that there has been quote 'great progress economically over the last seven and a half years,' " Obama told a Pennsylvania crowd.
"John McCain thinks our economy has made great progress under George W. Bush. Now, how could somebody who has been traveling across this country, somebody who came to Erie, Pennsylvania, say we've made great progress?"
The McCain campaign immediately took issue with the comment, noting the Arizona senator also said he knows families are facing "tremendous economic challenges."
"American families are hurting and Barack Obama is being recklessly dishonest," McCain spokesman Tucker Bounds said.
The McCain campaign has long argued Obama has a habit of twisting McCain's words. E-mail to a friend
CNN's Alexander Mooney, Rebecca Sinderbrand, Ed Hornick, Peter Hamby and Chris Welch contributed to this report.