Should Democrats worry that a blue wave is being treated like a sure thing?

Pretty much nobody, including his own staff, thought Donald Trump was going to beat Hillary Clinton in 2016, which made his victory all the more surprising.

We're starting to see perceptions of a new lock in 2018: that Democrats will see a wave and take control of the House of Representatives.

And that could be both good and bad news for them.

There's a good probability that so many people assumed Clinton would win in 2016 that they didn't turn out to vote. In hindsight, they might have. That's conjecture, of course, but it's not a radical idea to say that if Clinton had been seen as less of a lock, she might have generated more excitement.

But maybe because of that shocking loss, and with Trump in the White House, Democrats won't have to worry about setting lower expectations in 2018, according to Steve Israel, a former New York congressman who chaired the committee in charge of electing Democrats from 2011 thru 2015.

He said Democrats have "nuclear energy" right now.

"In environments like this, we used to worry that high expectations would lead to voter complacency," he said. "But 2018 has generated the equivalent of nuclear energy for Democrats. They're not staying home on Election Day, they're rushing to the polls. What Republicans are doing is bracing their donors for the worst, so that anything better than catastrophe can be spun as a victory."

Republicans, it's true, are predicting a wave could upend their majorities.

The House, where every seat is up for election, is much more likely to change hands than the Senate, where Democrats are defending 26 seats and Republicans are defending only eight.

Senate Majority Leader Mitch McConnell, a Kentucky Republican, was using hurricane terminology.

"This is going to be a challenging election year," McConnell told members of the Kentucky Today editorial board on Tuesday. "We know the wind is going to be in our face. We don't know whether it's going to be a Category 3, 4 or 5."

There is a very long list of reasons for Democrats to be optimistic. Here's one that CNN Political Director David Chalian rattled off:

They've won special elections in Trump country -- the Alabama Senate race and a Pennsylvania House district. When they didn't win special elections in places like Kansas, they significantly overperformed (for the most part) what Clinton did in 2016. They've been winning state legislative and judicial races by some surprising margins in places like Oklahoma and Wisconsin. Polls indicate that suburbanites, independents and white college-educated voters have continued to drift away from Trump and Republicans. Polls also indicate a plurality of voters favor Democrats over Republicans this November. Trump's approval rating hovers around 40%, and low presidential approval is historically a harbinger of gains for the opposition party. Democrats need a net gain of 23 seats to win control of the House -- and there are currently Republicans sitting in 25 Clinton districts. Long-shot challengers like Beto O'Rourke in Texas or Randy Bryce in Speaker Paul Ryan's Wisconsin district are raising eye-popping amounts of money.

Despite all of that, Democrats say they won't be coasting into November.

"Here's the bottom line: There's nothing easy about winning 23 seats under the current gerrymandered maps -- in the face of massive outside Republican spending -- and we're taking nothing for granted," said Tyler Law, the Democratic Congressional Campaign Committee's spokesman.

There's no doubt both parties will be working hard, but the problem for Democrats could be beyond their control in some ways, especially if the press and the public start to expect a Democratic takeover of the House.

Most Democrats think there's good reason for that expectation, at least right now.

"If the elections were held tomorrow, I think we would take back the house," said Rodell Mollineau, a former top Democratic Senate staffer and former president of the super PAC American Bridge 21st Century.

But he cautioned that political winds can change and pointed to the 2014 midterms, when Democrats felt good early on but Republicans ultimately saw gains in the Senate and House. He pointed out that national security issues, including ISIS and an Ebola outbreak, changed momentum during the campaign.

"There's always danger in complacency," he said, adding, "There are some things that are out of the control of Republicans and Democrats and especially on the House side that will contribute to voters' opinions."

In that vein, Democrats want to make the election about the more sensational aspects of Trump and his administration, his effort to dismantle Obamacare and the details of the unpopular tax law.

But Republicans, led by Trump, will try to make it about immigration and stoke the fears of the same voters who put him in office. The beginnings of that effort apparently came last week as the President turned to provocative rhetoric about the southern border.

Which means 2018 is just getting started.