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Editor's note: Julian Zelizer is a professor of history and public affairs at Princeton University. He is the author of "Jimmy Carter" and "Governing America."

(CNN) -- August is going to be a crucial month for President Barack Obama.

As the 113th Congress takes its recess, legislators will be returning to their states and districts to hear from constituents.

The stakes are particularly high for Obama and Democrats, who have one last chance to sway the House Republicans before two hugely important issues are resolved: the immigration bill and the budget.

As politicians in both parties begin to prepare for the 2014 midterms and think about the 2016 elections, this fall might be the last real opportunity for the president to win congressional support for these big measures.

Obama has made some progress in the Senate, where a small group of centrists in both parties has been mobilizing support behind compromise. The biggest challenge comes in the House of Representatives, where Republicans from solidly conservative districts have shown almost no interest in compromising on these issues.

The congressional "recess," like others that occur during the year, creates a huge window for citizens to make an impact on what legislators are thinking, as well as on what they will fear doing. As the columnist Ezra Klein recently wrote in The Washington Post, congressional "recess" is a misleading term since, "No one plays kickball. There aren't any juice boxes. ... They're still working."

While many politicians and pundits decry the fact that the recess period keeps getting longer, they serve an important role. The difference from the rest of the work year, Klein explains, is that legislators, who tend to work about 60-hour weeks during these off periods, focus primarily on constituent issues rather than on policymaking and fundraising.

Members of Congress start 5-week recess

Congress heads for recess

These kinds of activities include town halls, individual meetings and other civic events where citizens have a chance to make their voices heard directly.

It is true that Washington-based groups play a much bigger role these days in determining who comes out in these events, through what is called "Astroturf" lobbying, but still local citizens will be the main presence in these events.

Conservative voters will just be playing prevent defense this month. They will be coming out to these meetings to predictably voice their opposition to any immigration deal that includes a path to citizenship, and they will tell Republicans to stand firm on the budget and insist on the continuation of the cuts in domestic spending that were instituted by sequestration.

The administration has to counteract this pressure, or Republicans will return in September without any reason to say yes. Obama does have some allies in this battle, particularly on immigration. Business organizations that favor liberalized immigration policies are working hard to mobilize support in Republican districts so that voters can show that not everyone who lives in the red part of the map is against the bill.

They have support from prominent conservatives such as Karl Rove, who remains a major fundraiser for the party. Religious organizations are also joining the cause, as are immigration rights advocates who will make their voices known.

The Alliance for Citizenship, a coalition supporting the immigration bill that passed the Senate, plans to flood 52 districts and 360 events with their supporters. Clarissa Martinez-De-Castro of the group La Raza said, "There is one thing we must make absolutely clear and that is that the forces and the voices pressing for immigration reform are vast and growing ..."

With the budget, the administration's supporters face a more difficult challenge.

Yet even here, there are many Republican leaders, including House Speaker John Boehner, who have no appetite for a government shutdown in September over the budget, and they have strong incentives to encourage voters to come out to these meetings and call for a more reasonable approach to this ongoing standoff.

The Concord Coalition, an organization devoted to deficit reduction, has urged supporters to appear in districts to push for bipartisan compromise on a budget deal.

The odds are obviously not good that the administration can outflank the right. Nonetheless, we have seen how citizens can reshape the national debate.

In August 2009, tea party activists came out to town hall meetings to make their voices known on the health care bill. Their efforts captured national media attention and played a huge role in pushing their party to the right. While they lost on the final vote in Congress, the momentum from the town hall meetings that August created the political foundation for the Republican takeover of Congress in November. They have also driven the GOP toward a staunch stance on the budget.

There have been many other examples where citizens and activists used legislators' time in districts to convey a message.

Members of both sides of the Medicare and civil rights debates used these tactics in early 1960s to build pressure on members of Congress to pass or defeat the bills that mattered to them.

This month, Democrats, as well as those Republicans who believe that their party is headed in a destructive direction, might have their last big chance to sway the debate over these two issues, but they will have to do so by winning at the grassroots level and not in the Washington echo chamber where the conventional wisdom too often shapes political thinking.

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The opinions expressed in this commentary are solely those of Julian Zelize