My boy, Ezra, did an interesting exercise.
The idea behind the Laffer Curve is that there is some percentage at which revenue generated from income tax can be maximized. With tax rates at 0%, obviously no revenue is generated. At 100%, no revenue is generated because there'd be no reason to work. Somewhere between 0 and 100 is a sweet spot where federal tax revenue is maximized.
Ezra surveyed a couple economists and a bunch of politicians about where they think the Laffer curve peaks and presents their answers here.
Answers from Republican politicians and folks who lean to the right politically, tended to be well below 50%; Democratic politicians (looks like only two of them) were up around 70%. The two economists he asked identified top rates of 69% and greater than 60%.
Of course, as Martin Feldstein, Harvard, answered, maximizing federal revenue shouldn't really be a goal of tax policy, so in that sense the question is pointless. Further, half of the pertinent equation is missing when you ponder just the government-revenue-generation portion of the effect of tax rates. You should also be considering the effect on GDP or growth or something reflecting the effect on private sector income or wealth or something. But, still, the question is interesting for revealing how far apart are politicians' views. If you really believe setting income tax rates above 19% causes a drag on the economy, then of course you're going to fret about raising the top bracket from 35 to 39%. If, though, you think that you can raise rates to 70% without being an economic drag, then an increase from 35 to 39% for the top bracket is really not a big deal.