Four years ago, on a bright, cold Jan. 20, Barack Obama took his first oath of office as president and proclaimed a new post-partisan era. "The stale political arguments that have consumed us for so long no longer apply," 2009 Obama said.

The second four years of a two-term president's tenure are always different from the first, but it's hard to overstate how different this second term feels. Obama has most of the same goals, but in strategy and style, the change is dramatic.

Obama learned at least three lessons from his difficult first term, and they have reshaped his approach.

Lesson one: Confrontation sometimes works better than conciliation.

Obama hoped to be a bridge builder. But over the last two months, he's been more of a bridge burner.

He's told Republicans in Congress he refuses to negotiate over the debt ceiling, and he warned that if a showdown over the issue damages the economy, it will be on their heads.

He's dared them to shut down the federal government. "That's their prerogative," he said last week.

He's excoriated House conservatives in unfair, exaggerated terms as opponents of Social Security and Medicare. He's advocated new gun-control laws he knew Republicans would oppose. And he's ignored GOP opposition to his Cabinet nominees.

The combative strategy is the product of a theory that to get anything done in Washington, Democrats first need to (in their words) "break the fever" in the GOP and convince Republicans that refusal to compromise will lead them to political ruin.

"We've got to break the habit of negotiating through crisis over and over again," Obama said last week. "And now's as good a time as any."

Lesson two: Obama's a great campaigner but not always a great negotiator, so use him as Mr. Outside, not Mr. Inside.

The polite version of this lesson is that the president will spend more time enlisting ordinary voters in his battles - over the debt ceiling, gun control and everything else.

"You need to involve the American people in the discussion," his chief campaign strategist, David Axelrod, said last year. "It can't just be an inside game."

But it's also a reflection of an unwelcome discovery. When Obama tried to negotiate a grand bargain with House Speaker John A. Boehner, R-Ohio, in 2011, not only did the talks collapse, the failure dropped the president's popularity to the lowest point of his tenure.

From now on, negotiations with Republicans in Congress are more likely to be handled by Vice President Joe Biden - Mr. Inside, if you will - while Obama rallies public pressure.

That's why last week's announcement that Obama is turning his presidential campaign into a permanent network called Organizing for Action was important. The new group could give the president a mechanism for mobilizing supporters behind his priorities during the second term. A similar attempt didn't work in the first term, largely because the major legislation Obama sought then - an economic stimulus bill, a health care law and Wall Street reform - had to be negotiated through the "inside game" among interest groups.

Lesson three: Don't get over-ambitious.

In 2009, Obama began his first term with a huge electoral mandate and Democratic majorities in both houses of Congress. He also faced an economic crisis that demanded action. The new president aimed high with an agenda that included not only a $787 billion economic stimulus package but also health care and financial reform, and new legislation on immigration, education and climate change.

The last part of that to-do list stalled after Republicans won a majority in the House and vowed not merely to block any new Obama initiatives but to reverse what had already been passed.

This time, the president has trimmed his expectations.

"I don't presume that because I won an election, that everybody suddenly agrees with me on everything," he said in November. "I'm more than familiar with all the literature about presidential overreach in second terms." He has said he will pursue deficit reduction, tax reform, infrastructure spending, immigration reform and gun control. But it's not yet clear how much new legislation he can get through the GOP-held House.

Some of this was evident in Obama's inaugural address. He spoke about soaring hopes and national unity, as he did four years ago; it was still an inaugural address, after all.

But this time there were some steely notes as well, reminders to his opponents that he won the presidential election and that the voters were sending Washington a message.

The Obama who took his second oath of office Sunday is the same man he was four years ago, but he's a very different politician.

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