Editor’s Note: 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 Donald Trump has come to the end of another difficult political week for himself and the Republican party.

The fallout from his Helsinki news conference continues to shake the administration while the release of one of Michael Cohen’s secretly recorded audio tapes opened up new questions about the alleged payouts and cover-ups that happened during Trump’s campaign. Additionally, new polls show a Democratic lead going into the 2018 midterm elections, and Trump’s standing with key portions of the electorate, such as right-leaning college-educated women, is shaky.

But Friday morning there seemed to be a ray of hope for the administration. The President predictably turned attention to the best news that he and the Republicans can count on going into the midterm elections – the economy. Trump was pleased to announce that the 4.1% second-quarter growth is the best since 2014. The economy is roaring.

With an economy that is this strong, Republicans are hoping to enjoy a bounce that undercuts the negative news. If Americans vote their pocketbooks, the GOP might just contain some of the damage going into the midterm at a minimum – holding onto their majority even if it’s narrower. But just like in 2016, when the strong economy did not benefit the party in power, this midterm might be different. It is not clear that the economy will be enough to save the Republicans from the damage that President Trump has caused them through his time in office.

How can this be? Historically, midterms have often gone poorly for the party of the president irrespective of economic conditions. In 1966, the economy was very strong but President Lyndon Johnson’s Democrats saw the size of their majority shrink when they lost 47 seats in the House.

The economy also was growing in 1994, but that didn’t save President Bill Clinton from seeing Democrats lose control of the House and Senate. In 2014, the last time the economy was doing as well as today, Republicans regained control of the Senate.

Now, the multiple investigations into the Trump administration are continuing and accelerating. They are starting to produce some pretty big revelations, including the suggestion that then-candidate Donald Trump knew about the Trump Tower meeting where Donald Trump Jr. and Russian officials talked about getting possible dirt on rival Hillary Clinton. The President has denied that he knew about the meeting in advance.

It is likely that over the coming months, some of the benefits that a President and his party should naturally expect to enjoy from a booming economy might be undercut by the fears that this administration is corrupt and compromised. Voters might fear that the information we already have about wrongdoing is just the tip of the iceberg. And the images and sounds of Helsinki will not disappear.

While many Republicans still approve of President Trump, a majority of the country consistently does not.

The President has also turned this election into a referendum about American values. He has taken such polarizing stances on a series of key issues – hard-line immigration policies, his mockery of #MeToo, and his intransigence on gun control – that the energy driving his opponents will be stronger than the fact that economic times are good.

The irony of Trump is that his overwhelming and perpetual presence in the public square, with controversial and inflammatory rhetoric, might make it much harder for Republicans to keep voter attention on the economy. GOP candidates’ connection to Trump has made it difficult for them to win over suburban moderate districts.

As he attacks identity politics, more than anyone Trump has raised the questions of what is our national identity and what does this nation stand for in 2018? Voters will have to go to the ballot box, which hopefully won’t be hacked, and make a decision about what kind of country they believe in. Do the values that President Trump champions reflect the best of the nation’s ideals in 2018 or does the nation need a powerful check, through a Democratic Congress, to move us in a very different direction?

Finally, there is the complex nature of our modern economy, an ongoing story that weakens the connection between strong economic times and predictable political outlines. The fact is that there are large pockets of this economy where Americans are hurting. Even where unemployment is low, many families are struggling to get by, holding on to multiple jobs and unable to keep up with the obligations to pay for their children’s education or elderly parents’ health care.

This was an insight that was important to Trump’s campaign and it is a reality that Democrats can now use to their advantage – particularly as the President’s reckless trade war threatens many workers who are already at the brink.

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    A strong economy certainly should give Republicans some sense of confidence that they can perform better than expected in the coming midterms, but there is also more than enough reason to believe Democrats might still retake control of Congress.