The Obama administration’s top diplomatic and defense officials came to Capitol Hill Tuesday for concurrent meetings – one closed, one open – to answer lawmakers’ questions about the country’s Middle East strategy.

Secretary of State John Kerry huddled with Senate Foreign Relations Committee members in a closed session to talk about the Syrian conflict, while Defense Secretary Ash Carter and Joint Chiefs Chairman Joseph Dunford were publicly grilled by members of the Senate Armed Services committee on the country’s failure to quell the threats posed by the Islamic State or Russia’s intervention in Syria.

Not since it was selling Congress on the Iran deal has the Obama administration dispatched its foreign relations A-team to the Hill in such force to defend administration policy. And the meetings come at a particularly critical time.

Later this week, Kerry heads to Vienna for another round of peace talks on Syria – discussions that may include Iran, if Tehran accepts the invitation to join the American, Russian, European and Arab diplomats attending the meeting.

Meanwhile, U.S. officials have recommended that the White House back proposals to move U.S. troops closer to the front lines of the fight against the Islamic State in Iraq and Syria – a move that would represent a significant escalation, even if it wouldn’t officially put troops into combat roles.

The Obama administration is facing competing pressures from Congress. On one side are members who would like to see the United States engage in Syria more forcefully and take steps to elbow Syrian President Bashar al-Assad’s Russian and Iranian allies out of the way. On the other are lawmakers who want the United States to avoid steps that could lead to more confrontation.

Carter told the Senate Armed Services committee that the United States “won’t hold back from supporting capable partners in opportunistic attacks against ISIL or conducting such missions directly. Whether by strikes from the air or direct actions on the ground.”

The United States plans to focus its efforts on strengthening the anti-Islamic State campaigns focused on the group’s strongholds of Raqqah in Syria and Ramadi in Iraq.

But there is a complicating factor — the United States must contend with an engaged Russia heavily influencing the progress of events in Syria.

Russia’s involvement and influence in Syria is clearly a source of frustration for members.

“Secretary Kerry can take all the trips he wants to Geneva, but unless the military balance of power changes on the ground, diplomacy, as has been amply proven, will achieve nothing,” said Senate Armed Services Chairman John McCain (R-Ariz.), citing the example of the Syrian train-and-equip program.

“Only someone who does not understand the real problem, which is the underlying conflict in Syria and Iraq, or does not care to, could think that we could effectively recruit and train large numbers of Sunni Syrians to fight only against ISIL with no promise of coalition assistance if they came under fire from Assad’s forces,” he said.

“This is a half-assed strategy at best,” offered Sen. Lindsey Graham (R-S.C.), after asking Carter whether the United States would support a campaign to directly oust Assad.

Russian airstrikes, in the name of defeating the Islamic State, have appeared to be going after Western-allied rebel positions, but the United States has expressed reticence about taking part in any conflict that runs the risk of engaging Russia head-on.

Members are especially wary of Russia’s rising hegemony in the Middle East, and the potential for, as committee Ranking Member Jack Reed (D-R.I.) put it, “a potential great power struggle” on top of all the other conflicts coming to a head in Syria.

“We seem lost, and at confusion about what to do next, unable to put any real marker down or have any plan for success,” said Sen. Joe Donnelly (D-Ind.), wondering why the United States didn’t try to enforce some semblance of order with safe zones.

“I mean, at what point do we put a plan together, execute the plan, tell them what we’re going to do, and say stay out of the way?” he asked.

But Carter did not endorse the idea of establishing a buffer zone for civilians or a no-fly zone, which would be expensive, and, he argued, precipitate a direct conflict with Assad’s forces that the United States doesn’t want.

“We have sought now for some time, and continue to do, a political transition in Syria that would end the Syrian civil war,” Carter said. “We have not pursued a military solution to that.”

It is not clear how much progress can be made on the diplomatic front, while the parties meeting in Vienna later this week remain sharply divided on whether a post-conflict Syria should involve Assad.

Several lawmakers have urged the United States should drop back on that issue, at least until world leaders can broker an end to the war and stem the deluge of refugees escaping Syria.

But many other members continue to be vehemently opposed to Assad’s continued involvement, considering him to be more a cause of Syria’s problems than a potential partner in resolving them.