Top of the Laffer Curve?

Democrats have argued that current levels of taxation are far from the peak of the Laffer curve, implying that increases in tax rates could still bring in substantially more revenue. By contrast, Republicans have typically claimed that some rates of taxation are closer to the peak of the Laffer curve, or even potentially on the other side – implying that tax cuts (not increases) would raise revenue. So where is the peak of the Laffer curve, and where does America fall in comparison?