My political science knowledge is still at Amateur / College Student level, so I had to look that up.
Wikipedia pops up firstly - obviously - with their definition. It is:
...Major gains (that is, seats) made by a political party. Although there is no precise definition of what constitutes a wave election, the term is used in the United States when one party makes major gains in the House and Senate.
In a way, it doesn't involve the Presidency directly, although a Presidential candidate can influence or ride such a wave. Wave elections can happen in the midterms when it directly affects Congress.
What CAUSES a Wave election is also pretty obvious: Voter anger or dissatisfaction with how things are going. Problem is, which way do they direct that anger? And who stokes that anger to the boiling point?
We saw a good example of a Wave election back in 2010, when elderly white voters - just recovering from an election for Obama and the Democrats to overturn an incompetent Bush the Lesser administration and their Congressional enablers - were stoked by the Far Right media into a lobbyist-created "Tea Party" uprising. It overturned the Democratic gains of 2008 and led to the obstructionist gridlock of the last six years, during which even more anger against Obama and the government were stirred up by the Far Right to keep themselves in the game.
Thing is about anger: it is very hard to maintain. Oh, it is easy to stir one passions, but after the first few bursts of warmth you get from that rage you start looking at the actions you've done. And you start thinking through the gaps in logic that you jumped over while chasing after the objective that caused your rage in the first place. And you have to start thinking about repairing all the damage you did during your rampage. As a result, anger only gets you so far: It can get you into your political office, but it's not going to do you any good when you actually have to DO that job in office.
In terms of Presidential elections, a Wave election is only good for you when you have a need to gain or retain control of Congress when you get into the White House. For the Republicans, they don't need a Wave election for themselves as they've pretty much got the US House locked in via Gerrymander... but the Senate is up for grabs. Problem is, they are playing defense on the Senate: if there's any anger fueled towards the Senate, it'll be towards a bunch of Republican Senators refusing to do their jobs (SCOTUS vacancy, hint hint). It is possible there could be a great shift in Congress, considering how unpopular that branch has been, but Congress has been unpopular before and the Republicans were able to keep control...
If anything, using anger to generate a Wave election might backfire this time around: Railing against the failures of government could hurt you when your own party is clearly controlling said government. Despite all the deceptions, despite arguing against Democrats as destructive tax-happy libruls threatening TO TAKE YER GUNZ, a lot of voters know full well it's Republicans sitting in Congress doing NOTHING.
It doesn't help when your Presidential candidate running on a rage-fueled campaign - just guess what Trump did at his Connecticut speech last night? - is running on so blatant a racist, sexist, hate-driven platform to force a Wave election that he's causing a backlash. Not so much an ebb but a Riptide pulling away from the shoreline, sucking everyone else with him backwards into the deep ocean.
As such, this isn't a Wave Election at all. Is Riptide Election feasible? No, maybe Undertow works better.
I'd rather think that in normal circumstances this would have been a Legacy Election, where a sitting President with a popular base - and Obama's numbers are going up as the voters wake up to how he's actually done a good job despite the obstruction - could influence turnout to support his party's nominee: Get the voters who backed Obama in 2008 and 2012 to back his successor who would guarantee the gains made under Obama's administration survive (and even get upgraded).
But with all this anger - a lot of it generated by false accusations and driven by chaos - flooding the scene, it's going to be hard to focus on that Legacy. Which is probably what Trump wants.
Let's not let him have it. Turn this Wave into an Undertow. Stop Trump, and vote the Congressional Republicans out to sea with him. Flip the Senate, people. Screw gerrymandering, turn the House over to the Democrats. This is the type of election we need.