Arithmetic done under the constraints of politics is always suspect, and one should always examine carefully the claims of those seeking votes. But smart observers have learned to distinguish between the claims of political candidates and their advisers on the one hand, and proposals that have been evaluated by independent scorekeepers like the Congressional Budget Office on the other.

This principle has never been better illustrated than by the “budget analysis” put forward by Governor Romney’s chief economic adviser, Glenn Hubbard, in a recent Wall Street Journal column. Hubbard constructs a budget plan he imagines that President Obama might propose someday, engages in a set of his own extrapolations and then makes a set of assertions about it. He does not discuss President Obama’s actual plan or how it has been evaluated by the CBO. Nor does he invest his credibility in defending the claims that Governor Romney has made regarding his own fiscal plans – he simply states that, “Yes, President Obama and Mitt Romney have budgets with competing visions. But Governor Romney’s budget makes tough choices…” without delving into the specifics or trade-offs that Romney’s “tough choices” entail.

President Obama put forward a plan earlier this year that would reduce deficits by more than $4 trillion over the next decade. It would bring discretionary spending to its lowest levels since the 1960s. It includes $2.50 in spending cuts for every $1 in additional revenue. It also asks everyone to pay their fair share of taxes, repealing the Bush tax cuts for families making more than $250,000, and closing loopholes and shelters like preferences for private jets, hedge fund managers and offshore investments.

The independent Congressional Budget Office confirms that it would stabilize the debt as a share of the economy – thus returning us to a tenable fiscal path. It would do that while allowing increased investments in education, research and infrastructure that are critical to stronger, shared economic growth in the years to come. By focusing on building a strong economy for the future, it expands the tax base and reduces pressures for future tax increases.

But rather than criticize this approach, Hubbard ignores it – and instead chooses to invent a set of assumptions that bear no relationship to the president’s actual policies. His figures are not explained, but they apparently arbitrarily assume that the president must raise taxes to pay for spending above a level of Hubbard’s choosing.