By Liana B. Baker (Reuters) - Dish Network Corp has rolled out an advertising campaign suggesting a deal by a Japanese company to acquire Sprint Nextel Corp could threaten U.S. national security, hoping to sway lawmakers and win support for its rival offer. The campaign, which so far appears on the Internet and in Washington-area newspapers, is Dish's most public lobbying effort yet against Japan-based SoftBank Corp. Dish has been pushing the national security angle hard in Washington. ...