President Obama on Wednesday slammed opponent Mitt Romney and his running mate Rep. Paul Ryan (R-Wis.) for trying to sell a tax plan, which he dubbed “trickle-down snake oil.”

Addressing a crowd at a campaign event in Iowa on his final day of a three-day bus tour through the state, Obama elevated his rhetoric on his opponents’ tax plan, shifting slightly from the “trickle-down fairy dust” he called it a day earlier. 

{mosads}“They have tried to sell this trickle-down snake oil before,” Obama said at the outdoor event in Dubuque, where he was alongside first lady Michelle Obama in a rare joint appearance. “It didn’t work then; it won’t work now.”

The comments come as the presidential race has come to be labeled a “poisonous campaign,” with both sides exchanging daily barbs.

In his address, Obama accused his opponents of “being pretty dishonest about my plan, especially on Medicare” and he played both offense and defense on the issue, aiming to draw a stark contrast between his plan and his opponents’ proposal in an effort to lure the state’s seniors.  

“They are just throwing everything at the wall to see if it sticks,” the president said.

“Here’s what you need to know: I have strengthened Medicare,” Obama said. “My plan has already extended Medicare by more than a decade. Their plan ends Medicare as we know it.

“I have proposed reforms that will not touch your Medicare benefits, not by a dime,” Obama said. “Gov. Romney and his running mate have a very different plan — they want to turn Medicare into a voucher program.”

Mitt Romney’s presidential campaign, anticipating harsh attacks over running mate Paul Ryan’s Medicare plan, has hit Obama hard for cutting $716 billion from the program, in his signature healthcare reform bill.

But Obama sought to explain what his plan means. “I have made reforms that have saved seniors with Medicare hundreds of dollars on their prescription drugs,” he said.

The Obama campaign says the $700 billion comes from cutting waste and fraud and from reducing subsidies to insurance companies and insists the cut will not reduce services or benefits for seniors.

The Ryan Medicare proposals would shift the system to a subsidized private insurance model, which Democrats claim would hike healthcare costs for seniors.

The Romney campaign on Wednesday rejected Obama’s criticisms.

“President Obama has a long history of launching shameful political attacks on Medicare — but he’s the only person in the race who has actually cut Medicare,” said Romney spokesman Ryan Williams, in a statement to The Hill. “President Obama cut $716 billion from Medicare to pay for Obamacare and our nation’s seniors will pay the price with higher costs and fewer benefits.”

“As president, Mitt Romney will always protect this vital program for seniors and strengthen it for future generations,” he added.

Obama’s Dubuque speech also focused on the president’s likability, offering a rare glimpse at life inside the White House.

The president discussed tuning in to watch his wife make an appearance on “The Tonight Show With Jay Leno” on Tuesday night and said that the first lady will pick up their daughters from sleep-away camp on Thursday.

He also admitted to getting a little teary-eyed when he hears his wife speak.

“When I stand here and listen to her, I am reminded how lucky I am, because she is a woman of strength and integrity,” he said. “She is the best mom in the world, and she’s cute.”

The Obamas are scheduled to do interviews with People magazine and “Entertainment Tonight” before leaving Dubuque.

This story was updated at 4:27 p.m. to include a reaction from the Romney campaign.