Russia has since provided more information about Tsarnaev and his mother — both ethnic Chechens— that could have resulted in a more rigorous FBI investigation.
Obama pointedly said that Moscow has been cooperative "since the Boston bombings." He made no reference to information being held back ahead of the attack, but he did say, "Old habits die hard. There are still suspicions sometimes between our intelligence and law enforcement agencies that date back 10, 20, 30 years, back to the Cold War."
Russia has also stymied U.S. efforts at the United Nations to mount pressure against Assad's embattled government in Syria.
Assad has refused to let a U.N. team into the areas near Damascus and Aleppo where chemical weapons are believed to have been used. The White House says the team is standing by and could deploy to Syria within 48 hours if Assad allows it in. Given the unlikelihood of Assad giving the inspectors access, the U.S. says it is also seeking answers on its own and through international partners.
Polling suggests war-weary Americans are reluctant to see the U.S. get involved in another conflict in the Middle East. A CBS News/New York Times poll out Tuesday shows 62 percent of Americans say the country does not have a responsibility to intervene in the fighting in Syria, while 24 percent say the government does have that responsibility.
While Obama insists all options are on the table when it comes to dealing with Syria, the White House has little appetite for putting American soldiers into combat there. Even Arizona's Republican Sen. John McCain, who has pressed for aggressive U.S. involvement, has said putting U.S. troops on the ground in Syria would be a mistake.
Underscoring the danger that could await, the leader of Lebanon's Hezbollah militant group said Tuesday that Syrian rebels will not be able to defeat Assad's forces by themselves, suggesting the government's friends, including his Iranian-backed group would intervene on the government side if necessary.