The Neo-Malthusian Tribulation

I believe that the Deputy [McNulty] was not fully candid about his knowledge of White House involvement in the replacement decision, failed to disclose that he had some knowledge of the White House's interest is selecting Tim Griffin as the Interim U.S. Attorney for the Eastern District of Arkansas, inaccurately described the Department's internal assessment of the Parsky Commission, and failed to disclose that he had some knowledge of allegations that Tim Griffin had been involved in vote "caging" during his work on the President's 2004 campaign.

Monica Goodling Opening Statement, May 23, 2007

So, exactly what is "vote caging"?

Caging has also been used as a form of voter suppression. A political party challenges the validity of a voter's registration; for the voter's ballot to be counted, the voter must prove that their registration is valid.

Voters targeted by caging are often the most vulnerable: those who are unfamiliar with their rights under the law, and those who cannot spare the time, effort, and expense of proving that their registration is valid. Ultimately, caging works by dissuading a voter from casting a ballot, or by ensuring that they cast a provisional ballot, which is less likely to be counted.

With one type of caging, a political party sends registered mail to addresses of registered voters. If the mail is returned as undeliverable - because, for example, the voter refuses to sign for it, the voter isn't present for delivery, or the voter is homeless - the party uses that fact to challenge the registration, arguing that because the voter could not be reached at the address, the registration is fraudulent. It is this use of direct mail caging techniques to target voters which probably resulted in the application of the name to the political tactic.

Wikipedia