Are investors seeing the writing on the wall?

John Carney reports that Wall Street is now showing signs of turning against fiscal austerity.

Apparently, the Reinhart-Rogoff fiasco has something to do with it. Perhaps.

Or is it the realization that the narrowing US federal budget deficit since the start of the sequester in early March may signal the end of bountiful corporate profits?

As I've explained before, contrary to conventional wisdom, business profits are actually positively impacted by government budget deficits. Here is my take from a macro accounting standpoint:

Proof of this direct, positive relationship between government deficits and business profits is best demonstrated by manipulating the basic national income accounting identity in a manner consistent with the approach of economists John Maynard Keynes and Michal Kalecki. The following arithmetic demonstrates that government deficits have a positive effect on business profits.

Let Y=Total Output; C=Consumption; I=Investment; G=Government Expenditures; X=Exports; M=Imports; T=Taxes; R=Retained Earnings by Firms; Hs=Household Net Savings

Let the combination of the above (X - M) = Current Account Balance or Net Exports; (G - T) = Government Deficit; (Hs + R) = (Y - T - C) = Total Net Private Savings

To start off, here is the basic national income identity, as taught in all macroeconomic textbooks:
Y = C + I + G + (X - M)

Subtract taxes (from both sides of the equation) to achieve an equation "net" of taxes:
Y - T = C + I + G + (X - M) - T

Rearrange the equation to isolate total net private savings on the left side and to subtract taxes from government expenditures:
Y - T - C = I + (G - T) + (X - M)

Since (Y - T - C) can be broken down into household net savings (Hs) and retained earnings by firms (R), the equation can be stated as follows (see Krugman, 1994:313):
(Hs + R) = I + (G + T) + (X - M) 

...and can be rearranged as such:
R = (I - Hs) + (G - T) + (X - M)

In plain English, this translates into:
Firms' Retained Earnings = Investment - Household Savings + Government Deficits + Net Exports

The above equation clearly demonstrates that business profits are positively impacted by government deficits, net exports and private sector investment.* Household net savings, on the other hand, have the effect of reducing firms' retained earnings. Similarly, balanced budgets and government surpluses have either no impact on profits or have the effect of reducing them.

Now, it's true that under normal circumstances other factors such as household consumption and saving behavior and trade flows can significantly affect how these variables interact. However, in the current context where household spending has been largely subdued by deleveraging concerns, and exports weakened by sluggish growth in Europe, the UK and elsewhere around the world, the budget deficit consists of an important source of demand and (from a national accounts perspective) of corporate profits.