WASHINGTON : President Barack Obama ignited a new power showdown with Republicans Monday, vowing to fix America’s broken immigration system alone after Congress refused to vote on his top remaining domestic priority this year.

Obama rebuked Republican leaders who will not pass a “darn bill” because they fear conservative activists who oppose offering a path to citizenship for 11 million undocumented migrants as “amnesty.” If the lawmakers allowed a vote, “they would be following the will of the majority of the American people who support reform,” Obama said in a statement to reporters in the White House Rose Garden laced with sarcasm and bitterness.

“Instead, they have proven again and again that they’re unwilling to stand up to the Tea Party in order to do what’s best for the country.”

Obama said House of Representatives Speaker John Boehner told him last week that his chamber would not vote this year on comprehensive legislation that passed the Democratic-run Senate a year ago.

Searching for a genuine legacy-enhancing achievement to adorn his battered second term, the president argued that he thus had no choice but to act to stem a building immigration crisis.

“If Congress will not do their job, at least we can do ours,” Obama said, revealing he had asked the Department of Homeland Security to come up with recommendations within the next few months, which he pledged to immediately implement using his executive powers.

Obama said he would surge resources to secure the southwestern US border, where a flood of tens of thousands of child migrants from Central America has stretched customs services and deepened the partisan bile over immigration reform.

The moves will further inflame the fiery showdown between the Democratic president and Republicans ahead of mid-term congressional elections in November.

Republicans accuse Obama of exceeding his presidential power in a series of actions on health reform, immigration enforcement and personnel issues.

Their case was bolstered by a unanimous Supreme Court ruling last week that found the president overstepped his powers by appointing several officials to the National Labor Relations Board without the consent of Congress.

Obama’s salvo against Republicans came after the administration announced over the weekend that it would ask Congress for more than $2 billion to enforce the southern border and speed up repatriations of some of the 52,000 unaccompanied minors that crossed illegally into the country since October.

The decision will ensure that deportations are handled as humanely as possible, while still ensuring the protection of asylum seekers and refugees, the president wrote in a letter to congressional leaders.

The president also asked for additional authority for the Department of Homeland Security to process and remove unaccompanied child migrants from nations like Guatemala, Honduras and El Salvador who transited through Mexico.

Obama wants to surge immigration judges to the area and to do more to crack down on criminal and smuggling networks.

The request will also include funds for Central American nations to reintegrate returned migrants.

Obama campaigned in the 2008 and 2012 presidential elections for comprehensive immigration reform - racking up huge majorities from Hispanic voters, for whom the issue is deeply resonant.

The president said he was certain that Republican leaders did in fact want to move on the issue, but were unable to get their party’s rank and file on board.

He is almost certainly correct. Political analysts warn that Republicans cannot continue to alienate the rapidly growing Hispanic population and win presidential elections.

But the issue leaves Republican leaders deeply exposed among the party’s grassroots, and activists are whipped up every day by a chorus of invective about the reform bill on conservative talk radio and other forums.

Earlier this month, the number two Republican leader in the House, Eric Cantor, lost a primary nominating contest in his seat in Virginia in a shocking result largely attributed to conservative outrage over the possibility of reform. He quit his post as a result.

Political power players in Washington quickly adopted political positions after the president spoke.

“Speaker Boehner has made it absolutely clear that he won’t lift a finger to fix our broken immigration system, so President Obama is right to protect families from being torn apart,” said Senate Democratic Majority Leader Harry Reid.

Boehner said that he told Obama last week that the American people and their elected representatives did not trust the president to enforce existing immigration laws.

“Until that changes, it is going to be difficult to make progress on this issue,” Boehner said.