The timing of this week's G20 summit in St. Petersburg couldn't come at a worse time for President Obama.

When Obama heads to Russia Thursday for two days of meetings, he will be forced to face President Vladimir Putin — the man responsible for blocking United Nations action on Syria and hampering efforts to arrest National Security Agency leaker Edward Snowden — on his own turf.

The testy personal relationship between the two leaders, and their diverging agendas, has undermined the “reset” of relations that Obama engineered with former Russian President Dmitry Medvedev early in his first term.

Obama's relationship with Putin, an aggressive former KGB officer who has a natural aversion for the U.S., hit a new low when Russia gave Snowden asylum early last month.

The president responded by canceling planned one-on-one talks with Putin during the summit.

Obama also needled the Russian leader, saying he acted like a “bored” schoolboy with little interest in constructive dialogue during their previous sit-down at the G8 summit in Northern Ireland in June. Putin was reportedly infuriated by the comment.

And as Obama has sought to rally congressional and international support to enforce his “red line” ultimatum against Syrian leader Bashar Assad for using chemical weapons, Putin has staunchly defended the Russian ally.

Putin isn’t pulling his punches ahead of the G20 summit.

In an interview with the Associated Press published Wednesday morning, Putin again questioned U.S. intelligence concluding that Assad is responsible for the chemical attack that killed more than 1,400 outside Damascus on Aug. 21.

Putin said the charges seemed “completely ridiculous” and accused the Obama administration of failing to provide sufficient proof.

Over the weekend, as Obama decided to seek congressional approval for military action in Syria, Putin mocked the president’s status as a Nobel Iaureate, and past U.S. military interventions in the Middle East.

But if the White House is privately furious with Putin over his taunts, the administration’s public statements have expressed a desire to work with the Russian leader.

Instead of firing back at Putin, Secretary of State John Kerry on Tuesday pointedly downplayed the differences between the U.S. and Russia, as well as the inevitable clash over Syria at the G20 summit.

“I think it's important for us not to get into an unnecessary sort of struggle [with Russia],” he told the Senate Foreign Relations Committee.

More than once over the last two weeks, Kerry has given Russia credit for serious interest in a negotiated peace process in Syria.

In recent years, Russia also has cooperated with the U.S. on a new Strategic Arms Reduction Treaty and passing U.N. Security Council work to contain Iran's and North Korea's nuclear programs, Kerry stressed.

Kerry's emphasis on the positive may serve as an olive branch on the eve of a summit in hostile territory. But Steve Pifer, a senior fellow at the Brookings Institution and a former ambassador to the Ukraine, says it also has the benefit of being true.

Despite the public back-and-forth in recent weeks between Putin and Obama, Pifer says bilateral relations between the U.S. and Russia are rocky but nowhere near their low point of the last decade.

“People who suggest we are back in the Cold War with Russia have a short read of history,” he told the Washington Examiner.

Pointing to “all sorts of positives” since Obama's reset with Russia in 2009, he too cited cooperation on arms reduction, Iran's nuclear program and logistics on Afghanistan.

Back in 2008, there was even greater tension between Washington and Moscow after the Kremlin backed the breakaway republic of South Ossetia in Georgia. Some U.S. national security hawks pressed President Bush to conduct air strikes in support of Georgia’s government, which could have resulted in American war planes striking Russia troops.

Still, it's clear that if the White House had its way, this week’s summit would not be taking place in St. Petersburg this year.

“This is less a visit to Russia than a trip to the G20, which happens to be hosted by Russia,” a senior administration official told reporters.

While Syria will likely dominate meetings between leaders on the margins of the G20, and even most headlines, the formal agenda will focus on the importance of job growth at reducing global unemployment levels, senior Obama administration officials stressed.

The U.S. also will be seeking global support for measures preventing illegal tax evasion and tax avoidance — when companies use legal loopholes to reduce or avoid taxes.