Julian Zelizer is a professor of history and public affairs at Princeton University and a New America fellow. He is the author of " Jimmy Carter " and " The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society. " He also is the co-host of the podcast "Politics & Polls." The opinions expressed in this commentary are solely the author's.

(CNN) Donald Trump's presidency has already been filled with many points of drama, but his speech to a joint session of Congress this Tuesday presents him with a true monumental task. It takes place at a critical junction in his relations with an increasingly restive Republican Congress.

Trump's greatest firewall against the Democrats has been the fact that he enjoys a united Republican government. As of now, the GOP has been very reluctant to challenge the administration and generally remains optimistic about the political benefits that will accrue from this moment of Republican control.

Yet there are growing concerns among congressional Republicans that there has been little momentum in building a legislative agenda — other than some recent talk from Secretary of Treasury Steven Mnuchin about tax reform. Over the past month, President Trump has unleashed his blizzard of executive orders — yet Congress has been sitting around and waiting for the same kind of action on legislation. It is still waiting for a workable bill to come its way

This was supposed to be the Republican moment. But with a little over of a third of the Hundred Days almost over, Capitol Hill sounds like crickets chirping in the dead of night.

The early months of a presidency can be critical. Franklin Roosevelt, who would send 15 major bills to Congress by the end of his Hundred Days, had legislators working on an emergency banking bill just days after taking office. The Economy Act, which cut spending, passed a few days after FDR began work in the White House..

On the night of John F. Kennedy's assassination, Lyndon Johnson was already meeting with advisers to plan how he would move forward a massive tax cut and civil rights bill through the Senate, while mapping out a schedule for sending to the Hill a host of other domestic bills.

Notwithstanding the controversial election that brought him into office, George W. Bush was pushing within weeks for a massive supply-side tax cut and a federal educational bill to show that he would govern like he had a mandate. By the end of January in President Obama's first term, the House had passed a massive economic stimulus bill and both chambers had voted in favor of the Lilly Ledbetter Fair Pay Act. More importantly he was already working on health care and financial reform.

Meanwhile, the talk about repealing and replacing the Affordable Care Act has been just that so far -- talk. There are no bills to vote on. The first major bill that Trump signed happened earlier this month. It was legislation repealing rules that the Obama administration put into place requiring disclosure from energy and oil companies for payments that are made overseas. The bill is significant, but certainly far short of another New Deal. Republicans were forced to go back to their districts empty-handed to face angry protesters at town hall meetings.

Why is Trump moving so slowly on the legislative front compared with his nonstop pace on everything else? If you asked him, the President would certainly blame the Democrats. He would say that the Democrats are obstructing and delaying so that he can't get anything done. But the fact is that Republicans control the House and the Senate, so charges of obstruction make little sense.

And in fact it's not clear whether Trump even has much interest in the legislative process. This is where his background in business might not serve him well. Congressional politics is slow, messy, incremental and often frustrating. None of this is the kind of experience that Trump enjoyed in the world of business. The command-and-control structure of the corporation, where the CEO is boss, doesn't exist in our separation of powers, where the president has to work with or find ways to work through many other actors with fiefdoms of their own.

One House Republican lawmaker who supports Trump complained : "They are not reaching out to their allies here in the House and Senate. The danger is they become more insular and it creates more problems."

Trump's decision to fill many of his cabinet positions with people who have little experience in Washington doesn't help when it comes to the messy legislative process, either. Cabinet officials have often been instrumental early on in helping a president design his legislative proposals and strengthening support on Capitol Hill. While his Cabinet members are very conservative, many of them, such as Mnuchin and Ben Carson, are not well versed in the ways and means of D.C. or interested in building new policies. They are, as Trump's chief strategist Stephen Bannon told CPAC , interested in "deconstructing the administrative state."

The President hasn't seemed very interested in the core issue that brought him into office — jobs. Although after the election there was talk of a proposed infrastructure bill , the initial idea found considerable opposition when Democrats discovered that most of the money would go toward contractors and bankers rather than workers. Since then there has been little push for any kind of legislation, even though it would have been an opportunity to put the Democrats on the defense. Instead, Trump has focused on other issues, such as refugees, thus far pushing aside the one policy area that might allow him to start loosening the legislative barriers.

If Republicans get too restless, especially as they confront local protesters at town halls, they can easily start to cause problems with issues that Trump does tackle. Some might be more willing to investigate the controversies that have arisen, such as with Russia.

To be sure, the Hundred Days ain't even close to over yet. There is still more than enough time for Trump to start moving on the legislative front and to put his opponents in a defensive position. Tuesday's address to Congress serves as an opportunity for him to get this part of his term going. If he tries a rapid-fire approach, as he has done with executive orders, with legislation, then congressional Republicans will move the bills with speed and muscle. But he has to keep them on his side.

Most members of Congress understand that moments of partisan unity like the one Trump now enjoys are few and far between. Time is the most valuable commodity in American politics, and with every day the opportunities for passing legislation fall away.

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Trump needs to be careful right now. Many Republicans are clearly grumbling that the pace of the legislative agenda is not just halting but almost non-existent. Trump should not confuse partisan loyalty with love for him. The Republicans want bills to be sent their way. The longer he waits, the more that frustration builds and the more temptation there could be for the GOP to break with him. Then President Trump might find out, like presidents before him, just what Congress can do to a commander in chief they don't like.