From sequestration to horses and bayonets, voters are choosing between presidential candidates who have laid out vastly different plans for defense.

President Barack Obama has fleshed out his intentions for scaling back the U.S. Army and Marine Corps and shifting the focus of the Pentagon to the Asia-Pacific region. Republican challenger Mitt Romney has won kudos from the defense industry and Wall Street analysts for pledging to maintain the size of the Army and Marine Corps and build 15 Navy ships per year. But when it comes to executing either plan, both candidates will face the cold reality of Congress.

Dan Goure of the Lexington Institute writes that the Obama administration has “displayed a hostile attitude” toward the defense industry, insourcing private sector jobs in a careless way and overusing fixed-price contracting. “So bad has the situation become that the Pentagon is working to put out a new version of its Better Buying Power Directive,” Goure writes. “Just imagine what a second term would mean for government/defense industry relations.”

In Congress, Obama’s budget request has already met with a hostile reaction, with lawmakers sending the Pentagon back to the drawing board on reductions to the Air National Guard, thwarting Air Force plans to end Northrop Grumman’s Global Hawk and flatly rejecting calls for new rounds of base realignment.

If Obama is re-elected, Todd Harrison of the Center for Strategic and Budgetary Assessments feels that Congress may have an easier time avoiding sequestration, since both sides will have an incentive to reach a deal that forestalls the budget penalty, either the first year or even more than that.

But if Romney wins, Republicans in Congress have an incentive to delay a deal on sequestration, making it more likely that it will happen, Harrison says.

Romney has laid out an ambitious agenda for the Defense Department, vowing to increase spending and the number of Navy ships. Given the potential boost to Navy shipbuilding, Byron Callan of Capital Alpha Partners writes that General Dynamics and Huntington Ingalls Industries are likely to benefit from a Romney win.

But whereas Obama’s challenge is to get Congress to own up to budget realities, Romney’s campaign rhetoric will have to be reconciled with the same ground truths.

“The math will have to add up one way or another,” Harrison says, adding that keeping taxes low while increasing defense spending and not increasing the deficit may not be possible. “His intent may be to do all of those things. Which is it that he’s not going to do?”