You didn't get this from any Reagan economist. None of the Reagan economists ever claimed that tax cuts would reduce deficits. Martin Anderson wrote that they explicitly rejected the idea, calling it 'the myth of the supply siders'.
If they had believed such an idea, they wouldn't have sought spending cuts from Tip O'Neill, and President Reagan wouldn't have sought the tax increase he settled for in 1982. What the Reagan economists did say is that growth stimulated by tax cuts would recoup a portion of the revenue loss to the Treasury. Lawrence Lindsey's study found that nearly 2/3 of each dollar cut was recouped, which was in line with the predictions of the Reagan economic team.
The deficit is a political issue.
When the republicans forced slick willie to cut spending so the deficit could be reduced this was deemed a good thing.