From this story about the 287g program in the county containing Nashville, Tennessee:

Earlier this year, federal officials decided the Davidson County Sheriff's 287(g) program that screens the immigration status of incarcerated foreign nationals was targeting too many minor criminal offenders and not enough felons.

Davidson County Sheriff Daron Hall's controversial program is supposed to place a priority on screening foreign nationals who are accused of committing serious felonies, according to last year's revised 287(g) agreement between Metro and the federal government.

But internal U.S. Immigration and Customs Enforcement memos obtained by The Tennessean show that Hall's program was screening more than twice as many people with minor offenses as those with crimes such as murder, robbery and rape. An ICE memo from April shows that 73 percent of those screened by 287(g) in Nashville during the latter part of 2009 were arrested for minor offenses, while just 13 percent had been arrested for serious crimes...

...A second audit by ICE of Nashville's program from January through March of this year showed the numbers of those screened for minor crimes dropped to 36 percent...

...The series of ICE memos suggest federal officials were satisfied with the corrective action and that the Nashville program received no additional scrutiny.

The unanswered question is whether they were ignoring some major offenders to go after minor offenders; that doesn't appear to be the case. There certainly are only a limited number of resources to go around, but not going after minor offenders as the Department of Homeland Security wants means letting those who are or who might become major offenders off the hook and it's a form of de facto amnesty.

In any case, it's clear that to the Obama administration their use of 287g was too effective: they want as many somewhat law-abiding illegal aliens to stick around in the hopes of getting amnesty and converting them into voters for the Democratic Party.

Note also this:

Since 287(g) was put into place in 2007, the Sheriff's office has screened the immigration status of 12,486 foreign nationals cited and arrested for everything from murder to fishing without a license, according to data obtained in an open records request by the newspaper.

Of those, more than 7,250 immigrants have been processed for removal because of Nashville's 287(g) program. The sheriff's office could not say how many of those processed for deportation came from misdemeanors or felony arrests.