The key to being an effective politician is making the most damning charge possible about your opponent that the media will view as credible. The Republicans have been very effective in this respect because they routinely refer to President Obama's health care bill as "job killing" and use similar language to refer to other measures that he has pushed.
Serious reporters would ask the Republicans for evidence that the bill has actually killed any jobs. If the charge was true then the Republicans should be able to point to a sharp upturn in average hours worked per worker, as firms worked their existing employees harder rather than risk the cost of taking on a new worker. The Republicans would also be calling attention to the huge surge in temporary employment, as firms looked to temp firms for their workers rather than put workers on their own payroll. And, Republicans would note that the firms most affected, those employing near 50 workers (bigger firms almost all already provide health care and smaller firms are largely unaffected) are lagging other firms in employment.
Of course the Republicans do not provide this evidence because it does not exist. Average hours per worker is up somewhat from its low-point in the downturn, but it is still far below its pre-recession level. Employment of temps is also up slightly from the trough of the downturn, but it is still more than 20 percent below the pre-recession level. And it would be very difficult to find any evidence in the data on employment by firm size that mid-size firms are any more reluctant to hire than the larger or smaller firms that are less affected by the health care bill.
In principle, reporters have the time to investigate allegations like the claim that the health care bill is costing jobs. Readers on the other hand do not. If the Republicans can make an untrue assertion and simply have it passed along as a credible statement, because reporters do not do their jobs, then we should expect them to make even stronger statements. Perhaps we will soon be reading accusations from Republicans that President Obama and the Democrats are baby killers. After all, given the current practice of the national media, they would likely just pass the charge along as a reasonable statement about events in the world.