No, the surviving suspect in the Boston marathon bombing is not a good candidate for enemy combatant status. He is a good candidate for a good, old-fashioned criminal trial in a regular old American criminal court. Because what happened at the Boston marathon was fundamentally a crime. Yes, it was committed through the detonation of explosives, just like the Oklahoma City bombing. Yes, it terrorized those who were at the scene and in the city, just as the first World Trade Center bombing freaked people out. Yes, just as those and other incidents, it qualifies for the label "terrorism." (As in meeting the dictionary and statutory definitions; not as in involving Al Qaeda or some other organized group acting as some kind of war machine in an active, on-going campaign against the United States.)
And just like those other incidents, it should be handled by a civilian, criminal court. With a jury and a judge and defense attorneys and all of those pesky rights the Bill of Rights guarantees to all. (I'm not going to point out it guarantees those rights to all regardless of citizenship because this particular suspect is a citizen.) That anyone anywhere, let alone United States Senators, are even posing the question of whether this case should be handled in a regular old criminal court is terrifying. Of course it should. He's accused of committing a crime. As a person accused of a crime, he has rights. It is at all of our peril for us to suggest that the nature of the crime means he should not be treated like every other criminal defendant.
It's also terrifying that the Justice Department thinks the Fifth Amendment doesn't have to be followed in this case of a 19 year-old American citizen accused of committing a crime on American soil for reasons we can only guess at right now. We assume it's politically-motivated terrorism that might involve a wider conspiracy and might even be connected to terrorist organizations from other nations. Sure, could be. But this kook could also have been motivated by not wanting to disappoint an idolized older brother. He could just be a 19 year-old angry boy-man who wants to see the world burn. And even if it was politically-motivated terrorism, it's still a crime. The prosecution of crimes in this country, even really bad ones, are governed by certain rules. Rules we thought were so important, we enshrined them in our original founding document, our national charter. Originally, those rights outlined in the Bill of Rights weren't included in the Constitution, but it became clear that the Constitution wouldn't be ratified without them. Those who opposed a Bill of Rights argued that it wasn't necessary because the government wouldn't be able to violate those rights, but others insisted that if we didn't explicitly tell the government it had to respect certain rights, ultimately it would violate those rights. Seems the proponents were right not to trust government, but were overly-optimistic when they thought a written Bill of Rights would stop the government from ignoring those rights.
It is indefensible to treat this particular suspect as something special, someone different from every other criminal who has wreaked havoc and killed people.
The Columbine High School attack also involved explosive devices. I seriously doubt that anyone would have advocated labeling those perpetrators as "enemy combatants" had they been captured alive. No one thought about treating Timothy McVeigh as something other than a criminal defendant. Yes, those two incidents both pre-dated 9/11. But let's not pretend that the fact that these guys were all white guys born in the US doesn't factor in as well. Would we be talking about treating the surviving Tsarnaev as an enemy combatant if he hadn't been born somewhere else? If he didn't have ties to Chechnya, a region where organized terrorism is common? If his social media profile didn't list his worldview as "Islam?" It should bother us tremendously if his religion and/or nation of origin causes us to treat him differently.
Ultimately, I don't think whether this kid will talk with interrogators, even high value interrogators from the CIA, comes down to whether he is informed of his Fifth Amendment rights or not. If he wants to talk, he'll talk. If he doesn't, he won't. Lots and lots of bad guys have agreed to talk and have declined to "lawyer up" after hearing the Miranda warnings. I'm not convinced we gain much by refusing to respect the Fifth Amendment and the Miranda rule. But we lose a lot. We lose a lot of ourselves, of who we are if we allow our actions to be dictated by those who commit crimes against us. We never further our national interests by abandoning our most fundamental principles. If we allow those who attack us because they hate our most fundamental values to make us abandon those principles, well then those terrorists have won. And we let them.