INDIANAPOLIS (AP) — Chelsea just left. Barack and Bill are back. And look, here comes Hillary.

With less than a month until Indiana's May 6 primary, the Democratic presidential candidates and their surrogates are putting on a full-court press, wooing voters in more than a dozen cities over four days at a pace that's likely to get even more frenetic as the election countdown continues.

"If they would show up again even next week, I think the enthusiasm would still be there," said Allie Craycraft, vice chairman of the Delaware County Democratic Party. "It's been so long in Indiana since we've seen this type of excitement and the opportunity to have a pretty good voice in who it's going to be."

This week's trips include a six-city bus tour by Barack Obama, who started in South Bend late Wednesday and will wrap up Saturday in Muncie, and a southwestern Indiana swing by former President Bill Clinton. They come less than a week after 14,000 people attended a Dave Matthews concert in Bloomington supporting Obama and follow a three-day sweep of college campuses by former first daughter Chelsea Clinton.

Throw in a four-city swing by retired Gen. Wesley Clark, who sought the nomination in 2004 and now is stumping for Clinton, and Hillary Rodham Clinton's own three-city tour on Saturday and it's easily the most political activity this usually quiet primary state has seen in decades.

"The students have been very excited about having a piece of living American history walk into this building and provide a speech for us," said Phil Harrison, principal at South Vermillion High School, which was to host Bill Clinton on Friday. "Everybody is hoping for a handshake or a photo of some sort."

Six months ago, no one could have predicted that Indiana's 72 delegates would still matter come primary day. But a recent poll shows Obama and Clinton are running nearly even, and their campaigns say they are investing whatever time is needed to sew up the nomination.

"It is a necessity," Obama spokesman Kevin Griffis said of the Illinois senator's Indiana visits.

The Clintons have set a brisk campaigning pace across Indiana, each making multiple tours of the state. Former President Clinton was on a speaking tour of southwestern Indiana on Thursday before heading Friday to Clinton and Greencastle. Hillary Clinton, meanwhile, planned visits Saturday to factories with military-related contracts in Indianapolis and Mishawaka, followed by a session in Valparaiso with people who had worked at a closed factory.

Obama hit the state first on March 15, then went nearly three weeks between Indiana trips. He's now on his third swing but acknowledged in an interview with the South Bend Tribune that he's still getting to know Indiana voters.

"We had to spend more time in Pennsylvania because we were so far behind there, which gave Senator Clinton something of a head start in terms of campaigning across the state," he said.

The Illinois senator may have an edge in northwestern Indiana because of the nearby Chicago media market. But he's not as well-known in southern Indiana.

"We're going to have to do a lot more work south of Indianapolis to make sure that people have a sense of who I am and what I stand for," Obama told the newspaper.

Clinton's reach has been extended by campaign swings by Bill and Chelsea Clinton.

"They know her better than anybody else does and it is certainly an opportunity for us to utilize them to help get the word out about the solutions that Senator Clinton has put forward," said Jonathan Swain of Clinton's Indiana campaign.

Public interest in seeing the candidates appears high. The Obama campaign said Thursday it had already distributed all available tickets for its Friday and Saturday stops, where crowds of 2,000 to 3,000 people are expected.

"We'll probably do some of the bigger events, but right now we wanted to keep it a little bit smaller so he can hear from people," Griffis said. "When you get 10,000 people, it's not really a venue where you can ask questions and have interaction with the crowd."

The Clinton campaign expects to counter with more trips by all three Clinton family members, Swain said.