U.S. debt this week hit $16 trillion mark

NEW YORK (CNNMoney) -- Republicans are trying to make political hay of the fact that the federal gross debt this week crossed the $16 trillion mark.

But reaching that milestone was expected. And while notable, it overshadows the number that is of more immediate concern to Congress: the amount of debt subject to the legal borrowing limit.

The debt ceiling is currently set at $16.394 trillion. At the end of August, the amount of debt subject to that limit -- which excludes certain types of debt -- was $15.977 trillion, roughly $417 billion below the cap.

Since the government typically borrows between $100 billion and $125 billion a month, that means it's on track to hit the ceiling sometime in December.

But the Treasury Department will likely be able to use "extraordinary measures" to keep the debt just below the legal limit for a couple of months.

Bottom line: Congress will likely need to raise the ceiling in early 2013 or Treasury will risk defaulting on the country's legal obligations by failing to pay all of its bills in full and on time.

If the past is any guide, lawmakers will wait until the last possible moment to do so.

The issue has long been used as a political bludgeon by the minority party to paint those in the majority as irresponsible spendthrifts. Last year's histrionics were the most dramatic example.

Despite all the noise to come, the fact is the debt is the result of both parties' decisions over the years to commit to higher spending -- either because they approved new or expanded government programs or large tax cuts.

House Speaker John Boehner warned in the spring that Republicans would not approve another increase to the debt ceiling if it wasn't matched by a greater amount in spending cuts.

That will prove awkward since the House had a hard time coming up with $15 billion to pay for the highway bill, noted former Capitol Hill staffer Pete Davis. If lawmakers want to raise the debt ceiling to cover another year of expenses, they would likely have to increase it by more than $600 billion.

So Davis, who now runs Davis Capital Investment Ideas, expects Congress will instead pass a series of smaller, short-term increases to the debt ceiling as lawmakers duke it out.

Related: How Americans could be hit by cuts

Last year's debt ceiling grudge match ended up with a three-part debt ceiling increase that was matched by $2.1 trillion in spending cuts.

But $1.2 trillion of those cuts -- set to go into effect in 2013 -- are also the subject of much debate. They are mostly across-the-board cuts that many in both parties believe are a thoughtless way to go about reducing deficits. Yet they can't agree on how to replace them with a more sensible plan.

Add in disagreements over the expiration of the Bush tax cuts and other measures that threaten the economy, and it's clear Congress will have a lot of fights on tap after Election Day.