The Democratic presidential campaigns are delivering an onslaught of automated phone calls -- known as "robocalls" -- to Pennsylvania voters in the final days leading up to the state's presidential primary.
Many of the phone calls match the increasingly negative tenor of the race and boost the candidates credentials with key voting groups.
For example, Pittsburgh-area residents received a recorded message from Dick Lanzoni, a local sportsman supporting Obama, who portrayed the Illinois senator as a friend to gun owners and criticized his rival's record.
"I don't trust Sen. Clinton as much on issues that are important to sportsmen," says Lanzoni in the message. "Sen. Clinton voted to allow guns to be confiscated, and this raises real doubts." [Listen to the call.]
The vote Lanzoni refers to in the message is for an amendment to an appropriations bill banning the confiscation of weapons in times of emergency. Clinton was one of 16 Democratic senators to vote against it.
Lanzoni is a member of the Pennsylvania Sportsmen and Sportswomen for Obama Steering Committee. The group came to the senator's defense earlier in the month after the Huffington Post published Obama's controversial comment that small town Americans "cling to religion or guns" out of bitterness.
Lanzoni says that although he received the text of the message from the campaign, he believes every word.
The Clinton campaign unleashed its own deluge of negative robocalls, including one message criticizing Obama's vote for the 2005 comprehensive energy bill.
"Every gallon of gas takes over three bucks from your pocket," the male caller explains, "so why would Barack Obama vote for a Bush-Cheney energy bill that has put $6 billion in the pockets of Big Oil?" [Listen to the call.]
Both Obama and Clinton voted on the original Senate energy bill, but Clinton withdrew her support for the final bill after it came out of the conference committee. After the first vote, Obama stated that the bill would help his home state of Illinois by doubling the use of ethanol, and providing $85 million in subsidies for research on clean-coal technology.
Some election watchdogs and observers say they doubt the effectiveness of the thousands of calls going out from the campaigns and their supporters.
"The vast majority of people don't listen to them or hang up immediately when they pick up the phone," says Shaun Dakin, the founder of the National Political Do Not Call Registry, adding that the calls have "become so cheap that campaigns have become addicted to them, whether they work or not."
Dakin says that a remarkably high number of voters from the Pennsylvania area registered with his organization over the weekend, citing their displeasure with the calls they had been receiving.
Keith Staskiewicz is a freelance researcher for ABC News.