The most important time for the presidential candidates this week may be after Tuesday night’s debate.

True, the 90 minutes that they spend in the town-hall-style debate on Long Island on Tuesday night could be a game changer if one candidate performs terribly, as President Obama was perceived to have done two weeks ago.

But if the debate is seen to be more of a draw, then the winner will be decided in the hours and days after — with perceptions shaped by whichever campaign manages the post-debate time more effectively.

Here are five aspects both campaigns must consider:

TWITTER In the old days (meaning four years ago), campaigns would send e-mails to reporters during the debate, hoping to shape their coverage afterward. Years earlier, runners would drop printed news releases at each desk in the cavernous filing center where reporters covering a debate were working.

Now, both campaigns have armies of supporters posting on Twitter as soon as the debate begins. They are armed with hashtags and snarky observations as they seek to guide the early reaction to the debate.

Last Thursday, Republicans quickly seized on Vice President Joseph R. Biden Jr.’s grin. The week earlier, they were posting about Mr. Obama’s listlessness, even before the debate ended.

Neither side can control Twitter and its millions of users. But they can try to influence it.

THE SPIN ROOM But Twitter does not mean that the campaigns can forget about the journalists. The old-fashioned spin room — which used to be in a separate room from the reporters — is now just a designated area where campaign officials and surrogates eagerly make themselves available to reporters.

After Mr. Obama’s performance two weeks ago, Mr. Romney’s spinners were out in force, grinning from ear to ear. Mr. Obama’s advisers slinked out late, hardly able to contain their gloom.

The goal on Tuesday will be to shape the newspaper stories and the early-morning conversations, which can help to set the tone for the rest of the day.

THE CANDIDATES The best way to slow down a negative narrative — or enhance a helpful one — is to use the candidate quickly after a debate.

Two weeks ago, after Mr. Obama’s performance rattled his supporters, the Democratic campaign followed through with two huge, preplanned rallies. Despite the damage he had done to his campaign the night before, Mr. Obama was feisty and aggressive. That helped dampen the criticism a bit.

But there are risks. During the nominating campaign, Mr. Romney often stepped on his own success by making a gaffe the morning after a good debate or a primary night victory. Both candidates will need to avoid making any news that might take away from a victory.

THE ADS Most of the voters in key battleground states are not likely to attend a rally this week. However, they will see the ads produced by the candidates.

Mr. Obama produced an attack ad just hours after his debate with Mr. Romney, and another — an ad featuring Big Bird — a few days later. Mr. Romney went up quickly with ads promoting his five-point economic plan, to reinforce the idea that he has provided specifics to voters.

Bet on more ads — quickly — after Tuesday night’s contest.

MORE DEBATE PREP One big challenge for the campaigns will be the short amount of time between Tuesday’s debate and the final one, which will take place next Monday. The campaigns will need to try to shape perceptions from the first, even as they prepare for the next.

No matter how much the candidates and their staff members try to respond to the aftermath of Tuesday’s debate this week, they cannot forget the reality: Another is right around the corner.