Fred Barnes writes at The Weekly Standard:

President Obama and the Democrats have been ambushed. They blindly walked into the political trap Republicans set for them on Medicare.

Democratic strategists were certain that, with Paul Ryan on the Republican ticket, Medicare had become a better issue than ever for them. How do we know this? Democrats said so.

Ryan is the author of a Medicare reform plan that Democrats insist would “end Medicare as we know it.” That’s their mantra. Mitt Romney, who picked Ryan as his vice presidential running mate last week, has a similar plan of his own.

It didn’t occur to Democrats that Republicans might have devised, tested, and were ready to deliver a response that would put Democrats on the defensive. It’s a double whammy in which Obama and Democrats are held responsible for cutting Medicare spending and using the money to pay for the president’s unpopular health care plan, Obamacare.

Moving quickly, the Romney campaign packaged that two-step response into a crisp, 30-second TV ad [above] that began being aired yesterday. The campaign plans a large buy with the ad, particularly in swing states.

“You paid into Medicare for years,” the voiceover says. (A picture of an elderly man is on the screen.) “Every paycheck. Now when you need it, Obama has cut $716 billion from Medicare. Why? To pay for Obamacare. So now the money you paid for your guaranteed health care is going to a massive new government program that’s not for you.”

The National Republican Congressional Committee, the campaign arm of House Republicans, developed this response to Medicare attacks. It consists of this: defend and attack. First, defend the Republican plan to reform and save Medicare, then immediately go on the attack, citing the Medicare funds used to pay for Obamacare.