Washington (CNN) At the time in his tenure when most presidents fret over their waning clout, Barack Obama is redefining the concept of the lame duck.

His administration has been energized by his aggressive use of executive power. Some of the most hard-won achievements of his early years in office are beginning to pay off. And his political luck seems to be turning. With a term and a half behind him, Obama's prospects are brighter than they have been for years.

"We are on offense," said a White House official, who was not authorized to speak publicly, noting with satisfaction that predictions that the new Republican majority would grab the initiative and quickly make the White House a peripheral player did not pan out.

Though Republicans paint Obama's glass as half full, and argued that the administration is overstating its record, that hasn't rattled the man in the Oval Office.

The new sense of serenity in the White House solidified this week with figures showing that more than 16 million people have now signed up for health plans under Obamacare, the president's top domestic achievement.

That news came on the heels of booming jobs growth numbers and a tangible feeling that after years of slow recovery, things are looking up economically. The unemployment rate, at 5.5%, is at its lowest point since May 2008, before the Great Recession. And the U.S. economy is in much better shape than most of its rivals in the developed world.

Obama's approval

Also looking up, as a result, are Obama's approval ratings, which at a few points shy of 50% aren't exactly glowing but are not bad for a seventh-year president in the politically polarized capital of a divided nation. As recently as September, Obama was at risk of falling below the 40% level.

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There's a lightness in Obama's eyes and cocky defiance in his step in contrast to his slumped shouldered, hang-dog irritability of 2013, when the promise of his thumping re-election win the year before evaporated.

Second-term presidents often reach for legacy wins abroad, and Obama is no exception. He has defied Republicans and pushed forward on negotiations with longtime enemies Iran and Cuba, making good on a promise of outreach first made in a presidential debate way back in 2007.

Top administration officials now make the case that far from slipping into the ignominy of being a lame duck, Obama is actually dictating the political game, taking advantage of the GOP's teething problems with their new majority.

"Every time you pick up a newspaper or turn on the television, what you see is the Republicans are divided," said the White House aide. "We are the only ones that are doing anything proactive."

The White House believes that its initiatives on community college funding, the president's moves to regulate the Internet and actions to reshape the immigration system are delivering a political dividend, reasoning that many Americans are happy to see gridlock broken and the president taking action, a factor that might be partly reflected in Obama's better poll numbers.

Republicans

Republicans see it differently, of course. They believe Obama has engaged in executive overreach, taking steps unilaterally since he doesn't have sufficient support from the legislature. And they depict many of his actions as small-bore moves taken because they have successfully stymied so many other parts of his agenda.

Obama aides, though,think the GOP is the party with the weak hand. They believe that it's Republicans who have been the repeated losers in a host of recent battles: The showdown over funding for the Department of Homeland Security -- which ultimately saw it being fully funded despite Republicans' efforts to block funds for the implementation of Obama's immigration actions -- the siding of GOP lawmakers with Israeli Prime Minister Benjamin Netanyahu over Iran diplomacy and the current delay in confirming Attorney General-designate Loretta Lynch.

Obama, meanwhile, more relaxed than ever. He's speaking about race more freely than any time since he became president, notably in his speech on the 50th anniversary of the Selma civil rights marches earlier this month. And the White House counts a climate accord with China and a visit to India earlier this year as big wins for its strategy of rebalancing foreign policy towards Asia.

The GOP, for its part, is learning what the White House found out years ago -- that winning the Senate last year, and with it control of both chambers of Congress, brings its own problems.

GOP leaders have struggled to corral a restive coalition, as lawmakers who campaigned on the platform of repealing Obamacare and opposing the president's moves on immigration have clashed with leaders keen to show they can govern responsibly ahead of 2016 elections.

Obama has few such problems.

"He is completely unencumbered by politics, he will never have to run again," said a former aide, who worked for Obama for years, but spoke on background so as not to be seen as speaking for the current White House. "He does not have to worry about squishy members of Congress."

Spin

Republicans, however, respond that bullish White House assessments of its dominance are mere spin. They say that the administration is spending more time engaging in "locker-room talk" with reporters than pushing a serious governing program.

As Obama plots moves on his own, GOP legislators are demanding a say on a possible nuclear deal with Iran that could scuttle the diplomacy while Republicans countrywide are challenging the president's order to suspend the deportation of millions of undocumented immigrants.

And major Obama legacy-building initiatives that require the input of Congress are going nowhere slowly, in some cases because of opposition from within his own party, including on an effort to win authority to negotiate a massive Pacific trade pact and a bid to enshrine operations against ISIS in law.

"Maybe they should spend less time trash-talking and more time tending their own garden: Their party in Congress is currently filibustering a bill that would help prevent children from being sold into sex slavery -- and the President won't lift a finger. Think about that for a minute," said Don Stewart, a spokesman for Senate Republican Majority Leader Mitch McConnell.

The bill, which would protect victims of sex trafficking, has ground to a halt in the Senate as Democrats accuse Republicans of having slipped in an anti-abortion measure. White House aides are framing the dispute as another example of the GOP's inability to perform the most basic of governing tasks and get widely bipartisan anti-trafficking legislation passed. McConnell says he won't bring up Lynch's nomination until the sex-trafficking row is resolved.

And Stewart had further criticism of the White House: "As to their agenda, again, their own party is foiling the administration's efforts on things like trade agreements and war authority."

Bending the Constitution?

GOP leaders and some presidential scholars also warn that some of Obama's muscular political moves are not only vulnerable to be overturned by a future Republican president -- they may be bending the Constitution and against the law.

But aides say Obama has identified a volley of new executive moves for government agencies to keep the momentum rolling for months to come.

"It is incredibly important to have agenda items like that. Then you are not a lame duck," said the former aide, though he added : "I don't know how many more arrows like that are left in the quiver."

Still, whether it's fooling around with a selfie stick in a Buzzfeed video or rebuking Netanyahu from the Oval Office, there is new energy and purpose to Obama's presidency.

"I won both of them," a snarky Obama told GOP lawmakers in his State of the Union address, referring to his two presidential election victories. The implicit message: Despite the GOP's capture of Congress on his watch, he believes he also has a mandate to push forward his vision of change.

Struggle for relevance

Second term presidencies are not typically about aspiration. They're a grim struggle for relevance as the power of an administration inevitably fizzles.

But historian David Pietrusza argued that Obama is achieving something new by reshaping the notion of the lame duck presidency itself.

"(Obama) is not doing anything in terms of legislation, or very little," he said. "He has ratcheted up everything in terms of the regulatory executive order agenda."

Obama could argue that he is piecing together the most activist second term since the concept of the lame duck was enshrined by the 1951 enactment of the 22nd Amendment, which limited presidents to two terms.

Of the five lame duck presidents, Dwight D. Eisenhower and Ronald Reagan were aging and out of political gas by their seventh years. Bill Clinton was bursting with energy but mired in his impeachment drama. George W. Bush's administration was drained by long years of war and had no domestic agenda to speak of in its sleepy final years.

"We are not having the 2007 that George W. Bush had, or the 1999 that Bill Clinton had," said the White House official.