WASHINGTON — President Barack Obama’s hope of closing out his second term with legacy-shaping achievements on the world stage has invited the same bitter congressional opposition that has long thwarted his domestic agenda, producing a new power struggle that challenges the traditional limits of partisan battles in Washington.

The disclosure this week that Republican senators sent a letter to Iran about its nuclear program is the latest example of how Obama’s GOP critics have ignored the traditional deference to a commander-in-chief on foreign policy, while also reframing an issue of bipartisan concern in more starkly political terms.

The letter came days after Israeli Prime Minister Benjamin Netanyahu warned a rare joint meeting of Congress of the consequences of what he considered a “bad deal” with Iran.

Another point of contention is whether Congress should have a voice in approving any deal with Iran. Senate Republican leaders moved last week to start debate on bipartisan legislation subjecting any agreement to ratification by lawmakers, prompting Democrats to insist that the proposal be put on hold while talks proceed.

White House officials characterize the Republican strategy as reckless and partisan, designed to derail a foreign policy crafted by the Democratic president. They argue that the new level of attack on the president’s policy breaks with a decades-long practice of the U.S. speaking with one voice — the administration’s — on foreign policy.

“This letter sends a highly misleading signal to friend and foe alike that our commander in chief cannot deliver on America’s commitments — a message that is as false as it is dangerous,” Vice President Joe Biden said in an unusual and lengthy statement, adding that he couldn’t recall senators writing to advise another country during his more than three decades in the Senate.

Republicans say their reaction is guided more by the president’s lack of respect for Congress’ constitutional prerogative to advise and consent in foreign affairs.

“I will take blame for maybe Republicans being pretty aggressive,” said Sen. John McCain, R-Ariz. “But this president, unlike any other president I’ve ever known, is confrontational, noncommunicative, even to Democratic members of Congress. So you get a poisoned environment, almost the likes of which I’ve never seen.”

Party leaders view Obama, not Republicans, as controverting the post-World War II bipartisan tradition on foreign policy, said one Republican aide.

Public disputes between presidents and members of Congress over foreign policy are not new. Lawmakers have broadcast their contrary viewpoints repeatedly over the last century, on issues including the formations of the League of Nations and the North Atlantic Treaty Organization alliance, and the Vietnam War and U.S. policy in Central America.

In 1987, Democratic House Speaker Jim Wright of Texas waded personally into peace talks involving Contra and Sandinista leaders in Nicaragua.

And as President George W. Bush tried in 2007 to isolate Syrian President Bashar Assad, his administration sharply criticized Nancy Pelosi, the Democratic speaker of the House, for traveling to Damascus to meet with the beleaguered leader.

Netanyahu was invited to speak this month by Republican House Speaker John A. Boehner of Ohio, a move that brought complaints from the Obama administration, which was not told of Boehner’s offer ahead of time, as is custom for a visit by an elected foreign leader. Netanyahu in effect took the position of leading the opposition to an American president’s agenda.