Julian Zelizer is a history and public affairs professor at Princeton University, editor of "The Presidency of Barack Obama: A First Historical Assessment" and co-host of the "Politics & Polls" podcast. Follow him on Twitter: @julianzelizer. The opinions expressed in this commentary are those of the author. View more opinion articles on CNN.

(CNN) President Trump is turning heads again. After coming under intense fire for his stunning remarks, effectively siding with Russian President Vladimir Putin over the US intelligence community in Helsinki, Trump has doubled down on his rogue policies toward Russia.

After a few mild, confusing and halting assurances that he understands the risks Russia's cyber operations pose to our election system, the White House announced that the President would like to have Putin come to the United States for a second summit this fall.

And while Trump practices shock and awe diplomacy, the Republican-controlled Congress has been passing meaningless resolutions.

Today, by 98 to 0 , the Senate voted to oppose President Putin's proposal to interrogate some US officials. This resolution came soon after White House press secretary Sarah Sanders said that the administration was considering the possibility of allowing Russia to question Americans, including Michael McFaul, the former US ambassador to Russia. The idea rightly drew widespread condemnation and Trump finally said he disagreed with it. c

The former ambassador thanked the Senate for their unified stance against the proposal, tweeting , "98-0. Bipartisanship is not dead yet in the US Senate. Thank you for all your support."

There have been a few other signs of life from a dormant Congress. The Senate, for instance, took a similar step with trade when they rebuked the president's embrace of tariffs.

Yet the Senate should not be giving itself too much of a pat on the back.

While resolutions are an important step, relative to doing nothing, they are a weak use of legislative power against a president who has been extraordinarily aggressive in flexing his institutional muscle. They are just slightly more impactful than the sporadic remarks that senators like Jeff Flake or Bob Corker have made, which get attention in the media but don't amount to any substantive restraint on Trump.

If the Republican Congress wants to show that it is taking seriously the threats the President has posed, it has to show it is willing to take more tangible action. After all, with a slim 51 seat majority, any Senate Republicans who really want to demonstrate a profile in courage could refuse to vote in favor of the president's wish list.

It would only take a handful of Senate Republicans to block the confirmation of Brett Kavanaugh, the Supreme Court nominee.

If they want to take affirmative steps that put pressure on the President, they could also team up with Democrats to push for bipartisan legislation to protect the Mueller investigation from a president determined to bring it down. Additionally, Republicans could vote in favor of a substantive cybersecurity bill to address huge holes in our election system and the ongoing threat that we face.

Or they could conduct vigorous, televised oversight hearings to expose some of the problems taking place in the White House. Historically, hearings have massive effects on public debate about a president when done seriously -- think of William Fulbright and Vietnam, Sam Ervin and Watergate or Senator Inouye and Iran Contra. The hearings need to be public and they need to cover a broad range of issues that have roiled the nation.

Senate Republicans should be more resolute in pushing back against the kind of campaigns that have taken place in the House to delegitimate intelligence and law enforcement organizations. When the President kicks and screams about legislation they do send his way, as he did with implementing the Russia sanctions bill, they need to keep his feet to the fire with their oversight power.

Finally, Senate Republicans can't offer situational verbal support to the president when they believe that he is doing things that are fundamentally damaging to the republic. Recently, there has been an escalation in the angry reactions to Trump's actions -- such as Sen. John McCain saying that Trump gave "one of the most disgraceful performances by an American president in memory" in Helsinki -- but Republicans need to be more consistent in their opposition between now and the midterm elections. Otherwise, their words won't have much of an impact within the Republican electorate.

Follow CNN Opinion Join us on Twitter and Facebook

The Republican Congress has really reached an important historic crossroads. Given the highly dramatic and consequential developments that have taken place since day one of the Trump administration, the party will be remembered for how it responds and whether it does anything beyond passing resolutions and tweeting reprimands. If it does not, there will be no way to characterize the Republican Congress other than allied with the President, making them supportive participants in the era of Trump.