Barack Obama has only two years left in office but he is not ready to slow down. Instead, he plans to charge into two of the most sensitive issues in US politics: immigration and climate change.
Now faced with implacable Republican opponents in both houses of Congress, Obama will force the pace of reform using the executive power of the White House, risking a constitutional showdown.
Just back from an Asian tour during which he announced a deal with China to reduce greenhouse gas emissions, Obama now plans to issue a decree protecting millions of immigrants from deportation.
On both topics he is moving faster than America's Republican-led Congress would stomach, and his apparent determination to test the limits of his authority has infuriated his opponents.
On the environment. Obama believes his promises to Beijing -- a reduction in US carbon emissions by 26 to 28 percent from their 2005 levels by 2025 -- can be met without legislation.
On immigration, having seen many reform efforts stall on Capitol Hill, Obama thinks the time has come to act alone.
"I can't wait in perpetuity when I have authorities that, at least for the next two years, can improve the system," Obama told reporters on Sunday in Australia, after the G20 summit.
"I would be derelict in my duties if I did not try to improve the system that everybody acknowledges is broken," he said.
Without a coalition in Congress, Obama will not be able to reach a broad reform defining a path to citizenship for the millions of undocumented living and working in the United States.
But, some argue, an executive order could protect certain young people who grew up in the United States, were educated there or served in the US military from expulsion pending new legislation.
The extent of Obama's action has yet to be revealed, but the White House has said the order will be issued by the end of the year.
The Republicans, whose victory in this month's mid-term elections gave them a comfortable margin of control in the legislature, have expressed fury at this attempt to get around them.
"We're going to fight the president tooth and nail if he continues down this path," House Speaker John Boehner told reporters last week, warning that Obama would be in breach of the US constitution.
"This is the wrong way to govern. This is exactly what the American people said on election day they didn't want."
Some Republicans are working with Obama's Democrat supporters on immigration reform legislation, and his opponents have warned that executive action could poison this debate.
'President, not an emperor'
Another risk that Obama runs, as he himself admits, if he takes the solo route is that whatever he decrees with a single swish of his pen can just as easily be repealed by that of his successor in 2017.
Today's Obama also has another opponent of note: yesterday's Obama. When the president still had hope of negotiating a compromise on immigration reform, he opposed using executive decrees.
In February 2013, when a young activist begged him to intervene to stop families being separated by the expulsion of undocumented travelers, Obama said he was powerless to act.
"The problem is, is that I'm the president of the United States. I'm not the emperor of the United States. My job is to execute laws that are passed," he then declared.
Since June 2012, Obama's administration has chosen not to expel migrants who would have been protected by the DREAM Act, stalled legislation that would protect those who grew up in the United States.
And as late as September last year, Obama told Telemundo television that he could not go beyond the bill's narrow provisions without Congress passing legislation.
"What we can do is carve out the DREAM Act folks, saying young people who have basically grown up here are Americans that we should welcome," he said.
"But if we start broadening that, then essentially I would be ignoring the law in a way that I think would be very difficult to defend legally. So that's not an option."
But, in fact, Obama is reportedly now planning to go beyond what he said then was not an option.
According to the New York Times, citing administration officials, his decree will go beyond handing temporary papers to young DREAMers, but also cover the parents of US citizens and residents.
The number of undocumented migrants who could thus be protected from expulsion would rise dramatically from those foreseen in the act, up to around five million people.
Other presidents have used their executive powers to defer action on illegal migrants, but never on the same scale. Do the larger numbers change the political equation for Obama?
"Legally, the president is on firm ground. But in the world of politics, five million people is different," said Muzaffar Chishti of the Migration Policy Institute at New York University.
"This Congress will argue strongly.. that this is a direct violation of its political will," he warned.
But if Obama braves the political storm, he will get to kick the issue of broad legislative reform down the road for a future president to resolve -- perhaps one with a legislative majority.