But the key to his next 100 days could depend on his ability to work with Congress and show some proof that his policies will ultimately materialize into law — most importantly tax reform.

“I think the equity market no doubt is pricing in hope. … If we fast-forward to the end of the year, and nothing was done on taxes, I think this market gives up half of what we’ve gained,” said Leo Grohowski, CIO at BNY Mellon Wealth Management. Grohowski said his forecast is not scientific, but he would expect a chunk of the market gains since Election Day to start to evaporate.

“I don’t think this market is up entirely on fluff, but I do think that the economy that this administration inherited is due in large part to the aggressive stimulus from monetary policy. I think it was on a better footing, and that’s responsible for some of the gains we’re seeing,” he said. “Tax reform, regulatory relief and infrastructure spending — that’s the big three the market was taking away from the Trump election.”

Since Trump won the election, confidence among consumers and businesses has improved dramatically. Some of those readings, while still elevated, are off their highs. But in the meantime, some of the “hard data,” like jobs, retail sales and Friday’s first-quarter GDP have been coming in below forecast and point to a possible soft patch of growth.

“We need to see a convergence of the elevated confidence to the very anemic economy, and in order to keep the equity market moving forward, you need the convergence to be driven by better economic numbers,” said Julian Emanuel, equity and derivatives strategist at UBS. “We’re getting to the point where people are starting to wonder whether the potential that was reflected by the surge in confidence can actually be realized, which is why the next week or two in terms of the data is important, and we obviously want to see further progress on the policy front.”

S&P 500 performance in first 100 days, and election through 100 Days

Source: CFRA, data as of 4/26/17

The stock market, however, has been patient about the weaker economic reports. Economists expect the soft patch to end, and the second quarter should show a pickup, with growth closer to 3 percent than the first quarter’s paltry 0.7 percent. Corporate earnings are also showing surprising strength with profits up more than 11 percent for the first quarter so far.

The corporate earnings picture is certainly helping the market rally. Trump’s 11.4 percent since the election, compares with 18.3 for Kennedy and 12.3 for Bush. Kennedy’s 100-day gain was 9 percent, while Bush had a 7.7 percent rally, according to CFRA. Going back further, to the Depression in the 1930s, Franklin Roosevelt had an 86.5 percent gain in his first 100 days, and a 50.4 percent gain between the election and the end of his first 100 days.

Grohowski said what is surprising is how low the volatility has been with Trump in office, compared with expectations before Election Day. Since the election, Grohowski said there’s been only one day in 116 sessions, where the S&P 500 has declined by more than 1 percent.

Before his election, the market was apprehensive that Trump would create market turmoil, taking protectionist actions that would be negative for stocks. So far, while his administration has acted on trade, it’s been mostly in ongoing cases, such as the soft lumber dispute with Canada. The Trump administration put a 20 percent tariff on that lumber this past week, in a disagreement that has been brewing since the 1980s.

His rhetoric also has softened on Mexico, despite a tumultuous several hours Wednesday when the White House threatened to drop out of the North American Free Trade Agreement but then reversed it. Despite his pre-election vows, Trump also said he would not label China a currency manipulator, and he shows signs of willingness to work on trade with China, as he also calls on its help to deal with North Korea’s nuclear threat.

The president has also filled his days meeting with America’s CEOs, making it clear he wants jobs to stay in the U.S., but also to get rid of burdensome regulations, making it easier to do business and be more competitive.

This past week, he unveiled his tax plan, with a 15 percent corporate tax rate and a proposal to give companies a tax break to bring back cash stashed overseas. He also simplified individual tax rates, but both plans seek to remove deductions that will not be easy to eliminate. The House also has its own tax plan, cutting corporate taxes to 20 percent but including some proposals to provide to make up for the cuts.

While the White House tax plan is a step forward, the markets are still skeptical that it does not have a clear way to raise revenues, and it will not make it through Congress without a lot of modification, and possibly sparring.

But it was also seen as the opening round in what could be a long negotiating process and that as much as anything is a concern to markets. The failure of Republicans to vote on a bill to replace Obamacare in March suggests that there may not be the smooth sailing hoped for when Republicans won the White House and both chambers of Congress.

“For us, as long as progress seems to be made, as long as it’s tax reform and not a one-time tax cut, I think market participants would be more willing to wait,” said Grohowski, who said the market wants to see some action by the end of the year, or early next year .

As for whether the Trump rally will fall prey to the seasonal forces of Wall Street’s “sell in May” phenomena, Grohowski does not believe any losses would be deep, but the sell-off could come during the typically weaker months of the year.

“There may be some credence to that this year only because of how well the market has done. We never know what’s going to cause that 3, 5 or 7 percent pullback, but given how well the market has done, and how calm things have been, I think we could be in for a more disappointing late spring and summer. There’s no doubt the market might be ripe for profit-taking. We’re certainly not expecting any major pullback because we continue to see these pullbacks bought quickly. There’s a lot of dry powder out there,” he said.