Political conventions are usually fun times for the party faithful. Everything, including your wildest political dreams, seems to be likely rather than just possible. The opposition appears to be far less formidable than it appeared to be just a few days earlier. There’s nothing anyone can say that makes you think it’s not your destiny to win. Even your food tastes better.

[IMGCAP(1)]And you don’t have to think about actually doing anything. Not only does governing appear to be, at best, months away, but in the immediate afterglow of a convention, it’s hard not to completely believe in your candidates’ and party’s ability to deal with whatever lies ahead. Your only thought: Bring it on.

In fact, other than what you feel if you actually win on election night, when you’re a political junkie, this is your biggest political high and greatest sense of euphoria. But the truth is that, like most highs, this one won’t last long.

Nominated candidates and the people who support them absolutely are entitled to celebrate at the convention. But even if they take office at all, it won’t actually be for several months.

And though they would prefer not to, they really need to start to think about governing almost as soon as the convention ends.

This is especially true when it comes to the federal budget. In fact, unless there is a foreign policy problem or natural disaster that requires immediate attention, the federal budget will present the next president with his first big governing challenge. Getting ready to deal with it can’t wait until the nominee actually occupies the White House.

Part of the reason for this is statutory. The president is required to submit a budget to Congress between the first Monday in January and the first Monday in February. Inauguration Day is in the middle of this period and, although the outgoing administration could send a budget to Capitol Hill before it leaves, there is little incentive for it to do so.

The Bush administration has already said that it is going to follow this practice by only submitting a “budget” that shows what would happen if current law remained unchanged. This means that, other than the Pentagon and Homeland Security, the Bush 2010 budget will present no policy choices. It will barely be looked at.

That will leave it up to the incoming president to do all of the heavy lifting. Although no one will expect him to get a budget together in the less than two weeks between Inauguration Day and the first Monday in February, there will be a great deal of pressure on the new White House to get something to Congress as soon as possible thereafter. Waiting until later in the year when the Cabinet is in place and each department and agency is fully staffed won’t be an option.

Congress could start its hearings and deliberations without the president’s budget, but it seldom does. Even in 1995, when Republicans took control of the House and Senate at the start of then-Speaker Newt Gingrich’s (Ga.) era and said there was no reason for the president even to bother submitting a budget because they thought it would be irrelevant, Congress still waited for President Bill Clinton’s budget to be released to begin its public deliberations.

That same thing will happen in 2009. The new Congress, which at this point seems as certain as anything can be in politics to be controlled by the Democrats, will definitely wait for the president to submit a budget regardless of who is elected. Democrats will look to the first Obama budget as an opportunity to create momentum toward establishing their credentials for the next two years. They will wait for a McCain budget so that he has to take the political heat for what he proposes before Congress has to propose anything of its own.

So no matter who the president is, Congress will put pressure on him to get a budget to them as soon as possible. As a result, the president will have to start working on the 2010 budget even before his full economic team has been confirmed, or possibly even named.

There are two other reasons why the budget is likely to present the next president with his first real governing challenge.

The first is that the economy will still be the biggest issue for most voters in January. That will make the 2010 budget, where the new administration’s proposal for dealing with the economy will be displayed for the first time in one place for all to see, a critical factor. A well-conceived and solidly presented budget either will provide the White House with momentum on the economy throughout its first term or make its entire program harder to accomplish as people wonder what in the world the president could have been thinking.

The second reason is that, other than appointing the members of his Cabinet, the budget will be the first visible sign that the new president has taken charge. Everything from the color and design of the cover to the tables and presentation of the materials to the actual proposals will be scrutinized for clues about what this new president will be like and how he will govern. Because it will deal with the entire scope and breadth of federal activities, it will affect literally every industry, group, community and special interest in the country. Regardless of whether they supported the candidate in the election, the 2010 budget will be one of the primary reasons they decide whether they support the president.

So whether you’re in Colorado this week, Minnesota next week or just watching a convention from your home, keep in mind that the high you may be feeling won’t last forever. No matter how much you would like to keep them going, at some point very soon you’ll have to deal with the budget.

Stan Collender is managing director at Qorvis Communications and author of “The Guide to the Federal Budget.” His blog is Capital Gains and Games.