US President Barack Obama will send his diplomatic and defense chiefs to Congress Tuesday, intensifying a fervent effort to win crucial votes on supporting military strikes in Syria.
Secretary of state John Kerry and defence secretary Chuck Hagel will testify to the senate foreign relations committee in what will be one of the most high profile political set pieces in Washington in weeks.
Kerry, who used to run the panel and Hagel, a Republican who emerged as a fierce critic of former president George W Bush's Iraq policy, both know the ways of the chamber, as former senators.
The administration faces a daunting task in winning support for military action in Syria to punish it for a chemical weapons attack nearly two weeks ago.
Obama shocked the world on Saturday by announcing he would seek authorization for military action from Congress -- at a time when expectations of imminent US missile strikes on Syrian targets were running high.
Of the two chambers of Congress, the Senate is seen as the easier sell, as it is run by Obama's Democrats and contains a number of Republicans who have been pressing for military action.
The Republican-run House of Representatives however includes many conservatives who have blocked Obama's agenda across the board, and may be keen to thwart the president abroad, despite his warnings that US credibility is at stake, as it has already done at home.
Liberal Democrats wary of how voters will respond to another US entanglement in the Middle East may also be a worry for the White House.
Most of official Washington was on hiatus on Monday for the annual Labor Day holiday, but Obama was meeting with two of his most hawkish foreign policy critics, Republican Senators John McCain and Lindsey Graham.
Both men have repeatedly called on Obama to drop his reluctance to arming the opposition in Syria and to embrace more robust military action than the "limited" and "narrow" action the president envisages in Syria.
But both senators have reputations as mavericks and are sometimes pragmatic dealmakers across the political aisle, so their support for a strike would be a tangible victory for Obama as he tries to win over Congress.
The Senate hearing on Tuesday will take place ahead of the scheduled return to work of Congress on September 9 after a summer recess. However, there are no current plans for the House to be recalled before then.
Obama has a limited window this week for personal politicking on Syria, as he is due to leave town on Tuesday evening to visit Sweden and to go to the G20 summit in Russia.
Obama made calls over the weekend to individual members of Congress, as did Vice President Joe Biden.
Kerry, Hagel, national security advisor Susan Rice and military intelligence chiefs Monday held an unclassified briefing for Democratic House members on Monday.
A senior White House official said the administration would deploy all of its possible resources on Capitol Hill and beyond to sway opinion on Syria vote.
On Tuesday, before leaving for Europe, Obama will meet the chairs and top opposition members of key national security committees from both the Senate and the House.