MIAMI, Florida — Mitt Romney declined to say how he disagreed with his running mate on the issue of Medicare reform, despite taking three different versions of the question from reporters in a press conference Monday.

In the 72 hours since Romney tapped Paul Ryan to join him on the Republican ticket, his campaign has repeatedly insisted that he won't be adopting the Congressman's bold, and controversial, plan to turn Medicare into a voucher system, with aides saying he doesn't agree with his running mate on every issue. But asked where, exactly, he disagreed with Ryan, Romney demurred.

"The items that we agree on far outweigh the things we disagree on," he said, adding later, "I can't imagine any two people who have exactly the same positions on the same issues."

He went on to emphasize that he and Ryan agree that President Obama was wrong to cut $700 billion in Medicare spending in order to pay for the Affordable Care Act, and repeated that he would not change Medicare for those currently in the system.

"Instead, look down the road for the future, for young people coming along, let's make sure we're making promises we can keep," he said.

Romney has sought to draw energy from the sense of Ryan as a visionary without buying into details of his vision, a strategy that is now under serious pressure.

Asked whether the electorate was ready for major reforms to the program, Romney said, "I can't tell you about the politics of something like the Medicare issue, but I can tell you about the truth. The truth is we simply cannot pretend [that being] on track to become bankrupt is acceptable."