The man at the centre of a possible military conflict with Iran over its nuclear program, the Israeli Prime Minister Benjamin Netanyahu, is visiting the White House.
No doubt the leaders are keenly aware of the global, regional and personal implications of the meeting.
The president and prime minister are not political soul mates.
The last time the leaders were together in the Oval Office, Mr Obama endured an all-too-public lecture on Middle East peace, so the tone when they get together will say a lot about the substance.
High-level meetings can be pro-forma. This one will be anything but.
In their discussion, the first issue is about "time and space", as the president termed it on Sunday in a speech to the pro-Israel Aipac conference in Washington.
Israel's Defence Minister Ehud Barak has talked about a "zone of immunity" beyond which Iran's nuclear programme will be dispersed, underground and difficult to attack.
While Israel may be flexible regarding the timing of a strike, it is sceptical that sanctions and diplomacy will succeed without military action that first stops Iran's nuclear advance.
The Obama administration does not believe Iran has made the strategic decision to build an actual weapon, which means - as the president said on Sunday - "an opportunity still remains for diplomacy - backed by pressure - to succeed".
The existing course of political isolation and "crippling" sanctions is gaining momentum and taking its toll on the Iranian economy.
Iran acknowledges the rising costs and appears prepared to bear them. Its nuclear progress has not been linear (actual and virtual sabotage have played a role), but as long as centrifuges keep spinning, Iran figures time is on its side.
Tehran recently agreed to return to international negotiations, perhaps trying to forestall an attack, position itself as the potential victim of Israeli and/or US aggression, solve the problem on acceptable terms, or all of the above.
The second issue is about tactics, specifically what might happen after a military strike.
If Israel launches a pre-emptive strike, it anticipates a limited retaliation, most likely a barrage of missiles from Iran - and perhaps Hezbollah sooner - and further attacks on Israeli interests around the world later.
But Israel also points to two previous pre-emptive plays, Iraq in 1981 and Syria in 2007, where neither country retaliated overtly against Israel. They also did not resume nuclear activity to the pre-attack level.
The Obama administration is far less sanguine that the impact can be controlled. "A strike at this time would be destabilising," Gen Martin Dempsey, chairman of the Joint Chiefs of Staff, said last week.
The Middle East is unhinged right now, US thinking goes. Whatever the blowback in Syria, Lebanon, Gaza, Egypt or Yemen, it cannot be good for Israel or the United States.
Public opinion, now more populist, would undoubtedly side with Iran and re-open a still-raw wound from Iraq that America is at war with Islam.
And there are still 89,000 US troops in Afghanistan, an inviting target for Iran-backed insurgents right next door to Iran.
Even a targeted strike against Iran's nuclear facilities and a measured Iranian retaliation risks a wider conflict.
All of which impacts the global economy. Energy experts suggest there is already a 10-15% "Iran premium" on the price of oil, even before a shot is fired.
Should there be military action, oil prices will spike dramatically. A pivotal economic domino, Greece, is heavily dependent on Iranian oil.
A blockade, severe spike or implosion would put the global financial recovery in jeopardy, not to mention Mr Obama's core re-election message.
The final issue revolves around what Iranian nuclear end-state the US and Israel can live with. This is where a disagreement between Jerusalem and Washington is most likely.
Without clear evidence Iran is building a nuclear weapon, a pre-emptive attack would essentially be a preventive war - a concept largely discredited after the Bush administration rhetoric in the run-up to the invasion of Iraq proved so wildly off the mark.
Israel and the US have made effective use of President Mahmoud Ahmadinejad's pledge to "wipe Israel off the map".
But how certain is the eventual leap from a civilian to a military programme and a nuclear warhead? The intelligence today is as murky as it was prior to 2003.
From an Israeli standpoint, since the distance between civilian energy and a bomb beco mes shorter as times goes on, even enrichment for civilian purposes is unacceptable.
A permanent solution requires Iran's centrifuges to stop spinning. This is the US preference as well.
Iran is entitled to a civilian nuclear programme, but the US negotiating position would require Tehran to forego enrichment and eventually get the nuclear fuel it needs from a supplier like Russia.
But Iran does not trust that the international community will ever be a reliable supplier. My Penn State colleague Flynt Leverett believes Iran sees its nuclear efforts as a catalyst for scientific innovation, not unlike how the US viewed its space programme 50 years ago.
Thus, Iran is unlikely to negotiate it away and appears to be racing to achieve a de facto civilian enrichment capability.
It is unlikely Israel could tolerate such "nuclear ambiguity," but what about the United States?
In an interview with The Atlantic timed with the Netanyahu visit, the president stressed again "it is unacceptable for Iran to have a nuclear weapon."
But he noted recent comments by the country's Supreme Leader Ayatollah Ali Khamenei that an actual bomb is "haraam", meaning sinful and forbidden by God.
Put this together with another comment by Gen Dempsey that Iran is a "rational actor," and it suggests that the United States is prepared to contain (no US official will use this word) an Iranian nuclear programme that remains south of an actual weapon.
Ostensibly, Iran could retain an enrichment capability subject to heavy scrutiny by the IAEA, the UN nuclear watchdog. Military action would remain on the table but, without a threatened breakout, stay there.
"There is too much loose talk of war," Mr Obama told Aiapc. He clearly wants to push military action at least past November.
Mr Netanyahu will probably trade time now for a US commitment to act down the road. As Daniel Levy wrote last week in Foreign Policy, for reasons of capability and geo-politics, Israel would prefer the mission be conducted by aircraft sporting the stars and stripes of the US rather than the blue and white of Israel.
But if President Obama sticks to his current position, with military action a distant prospect as long as Iran crosses no red lines, the prime minister might decide to take a shot at Iran sooner.
If that happens he will draw the president into an incredibly complex crisis that he did not start, may or may not have been informed about in advance, believes is premature and whose outcome he can not control.
All of this, potentially, in the middle of a presidential campaign.