As expected, President Obama was the primary target of attack, but so were the Republicans at the other lecterns.

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The 26-year-old, who was killed in a shootout with police last week, and his younger brother, Dzhokhar, 19, are the primary suspects in the attack, which left three dead and more than 250 wounded.

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That was a safe assumption until the Florida primary, when two things happened: Romney proved he could attack his opponents, and Romney, who had never pulled even 40% of primary voters in other states, won 47%.

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Initially, their primary purpose was to offer protection from attack.

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The primary task for law enforcement after such an attack is to identify the perpetrator(s), apprehend them, and examine whether this attack was a one-off or the first in a series.

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And they came to attack Specter -- who eventually lost his primary -- as the embodiment of all that was wrong with Washington.

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Each attack or block also builds the power meter, which has three primary uses.

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The threat of an EMP attack was not taken seriously by US military planners during the Cold War because they were concerned with the primary Soviet threat to annihilate the US and its allies by launching several thousand nuclear warheads against them.

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