DENVER -- Several of Republican John McCain's prospective running mates campaigned Monday for their presidential candidate as the Democratic National Convention opened in Denver.

McCain is expected to announce his No. 2 as early as the end of the week before his party meets for their nominating convention in St. Paul, Minn., next Monday.

Here's a look at the whereabouts of the Arizona senator's possible choices for vice president:

--Tom Ridge, a former Pennsylvania governor who was the country's first Homeland Security secretary, was working at his Washington, D.C. consulting firm, and had no public events scheduled, said Michele Nix, his spokeswoman.

--Minnesota Gov. Tim Pawlenty spent his third day on a tour of battleground states to the east. He was set for a trio of Ohio events promoting McCain -- one at a factory, another in a high school cafeteria and the third at a hotel fundraiser.

--Former Massachusetts Gov. Mitt Romney was attending a McCain fundraiser in Newport, R.I., before heading to Denver. He planned to be at the site of the Democratic National Convention on Tuesday to lobby for McCain.

--Connecticut Sen. Joe Lieberman, an independent who caucuses with Democrats and is said to be on McCain's short list, said Monday that he and others close to McCain should take a "vow of silence" concerning the vice presidential nomination. He spoke to reporters after a speech to a business group in New London, Conn. He said he doesn't expect to be offered a spot on McCain's ticket, but he won't discuss his chances.