(n.) - A behavior of the mainstream media during an election campaign, characterized by a period of widespread silence concerning a news story that is severely embarrassing to a liberal candidate. The silence ends when it no longer shields the candidate from damage.
The Swift Boat Hush is named for the 'Swift Boat Veterans for Truth'. This anti-Kerry group began a major advertising campaign during the 2004 US presidential campaign on August 4, 2004. Most major newspapers (and the Kerry campaign organization) refused to discuss these charges until about 2 1/2 weeks later, when it became apparent to them that the charges were seriously harming Kerry in the polls.
Another example is the coverage of the 2006 special election in California's 50th congressional district, when 5 days before the election the Democratic candidate was recorded telling a group of illegal aliens that "You don't need papers for voting." Many major newspapers did not print this quote until after the election.