Three weeks past Election Day, and already it’s starting to feel like campaign season all over again.

Political billboards and bus shelter ads are back. Petition drives and e-mail action alerts have returned. Not even the Macy’s Thanksgiving Day Parade was immune from the latest barrage of political advertising about the dangers of the “fiscal cliff.”

A coalition of union groups aired ads during the NBC broadcast of the parade in a number of key states, urging Congress to resist cutting entitlement programs. Since Election Day, another group, the National Coalition to Preserve Social Security and Medicare has collected 65,000 signatures, also urging Congress not to meddle with the retiree programs.

The debate over what Congress should do to avoid the troubling consequences of a series of tax hikes and spending cuts set to hit at the end of this year has underscored the intensity of the nation’s political divide, and the speed with which the partisan machinery can now shift gears from one big fight to the next.

Within days after the November election, the bus shelters and billboards were taken over by a group called Fix the Debt, which is urging a bipartisan deal to avoid the cliff.

All of that attention has the potential to change the character of dealmaking now beginning in the lame-duck session of Congress, which is faced with a series of monumental decisions about the nation’s fiscal future.

There appears to be little chance that even a post-election populace preparing for the holidays would miss it if lawmakers cast unpopular votes as part of a deficit-reduction compromise.

With the next election two years away, lawmakers have traditionally felt more free to take difficult votes during post-election sessions. In some of the busiest lame ducks, one party was about to lose its power — and sought to make a deal while it still had the power.

In 1994, the recently defeated congressional Democrats helped pass a massive trade deal. Just two years ago, Vice President Biden and Senate Minority Leader Mitch McConnell (R-Ky.) worked in near secrecy to hatch a deal to extend the George W. Bush -era tax cuts — now expiring again. House Democrats, dislodged from their majority in the midterm elections, grudgingly but quickly signed off.

This lame-duck session, however, will offer legislators less cover than usual. Few previous sessions have been as closely watched by outside groups, and none has ever occurred under the present level of moment-by-moment scrutiny made possible by cable news and social media.

“People are yearning for and very interested in a much more transparent process,” said John Hishta, a top official with AARP, which has urged Congress to avoid major entitlement cuts in the condensed hothouse of a lame-duck session.

Max Richtman, president and chief executive of the National Coalition to Preserve Social Security and Medicare, said people are following developments so closely that the organization now tweets its supporters before and after each meeting their lobbyists hold with lawmakers.

“I detect more interest, not just in waiting for something to be resolved and finding out what happened, but in participating in the process,” Richtman said.

Polls bear out the extraordinary interest the public is bringing to bear.

A survey released by the Pew Research Center last week showed that 33 percent of Americans said they were “closely following” the debate over the fiscal cliff, more than were following CIA Director David Petraeus’s resignation or the fighting between Israel and Hamas.

That number only marginally trailed the 40 percent of people, Pew found, who were closely following news about the election in late September.

The fiscal cliff is “something that folks out there would be aware of and would be concerned about,” said Michael Witczak, a professor at Catholic University and one of a number of clergymen nationally to recently deliver sermons that touched on themes related to the congressional debate.

In a homily delivered at the Shrine of the Most Blessed Sacrament in upper Northwest Washington, Witczak cited the congressional crisis, as well as Hurricane Sandy, as causes of “tribulation and distress” among the parishioners, who include members of Congress, federal workers and members of the media.

The message was that crises force people to think about what is most important to them, and that they should lead Christians to trust in God.

That interest level is being driven, in part, by the media, which has moved as quickly as interest groups to fill time and print once consumed by the minutia of a presidential campaign with stories of Congress’s latest clash.

Already, a local Washington station has unveiled a countdown clock, ticking off the days until $500 billion in tax increases and spending cuts will hit without a congressional deal to avoid them.

Democrats, in particular, have been anxious to ensure their supporters remain in the game after their November wins. President Obama’s campaign apparatus has been encouraging supporters to turn their efforts to lobbying Congress to extend tax cuts for the middle class and allow them to expire for the wealthy.

In 1933, the country actually passed a constitutional amendment — the 20th — intended to end sessions where law is made by the defeated and the departing.

It required a newly elected Congress to arrive quickly after the start of the new year to take over. In a time when travel was difficult, people figured no one would want to return to Washington to fight things out around Christmas.

But they never met the modern Congress, which has perfected the art of doing big deals between Election Day and New Year’s.

“Two years is forever in American politics. Two years before the voters come back to [the polls], they strike a deal,” said Bruce Ackerman, a Yale Law School professor who has studied lame-duck sessions. “To say that this is good is to say that democracy is bad. . . . It’s as simple as that.”

Those sick of the ads may be distressed to learn that advocates on both sides of the political divide said Monday that they are marshalling their resources for the debate this month — aware that Congress’s year-end debate is probably only a prelude to a much broader fight over entitlement reform and tax changes in 2013.

“If history repeats itself, they’re going to kick the can down the road. Nothing real is going to be solved before the end of the year,” said Matt Kibbe, president of the conservative group FreedomWorks.

Better, then, to save some of his group’s energies until 2013. “That’s when the real opportunity is.”

Peyton M. Craighill contributed to this report.