While we can't be sure what will happen, most evidence suggests that there will indeed be a blue wave sweeping the House of Representatives this November.  Most elections since November 2016 have been won by Democrats, and even when Republicans win, the Democratic candidate performs better than expected.  There is an enthusiasm gap between the two parties.  Many Democrats are extremely angry and fired up to vote by anti-Trump hatred, while many Republicans are apathetic because Trump hasn't accomplished much of what he promised.  Disillusioned Trump voters may stay home, while angry anti-Trump voters go to the polls. 

Considering that the Democratic Party is steadily moving further to the left, a blue wave could have serious consequences.  That being the case, what steps do Republicans have to take in order to win in November? 

To begin with, Republicans should not campaign on low taxes.  Many Trump-supporters don't care about low taxes, especially the ones who voted for Trump after voting for Obama.  Campaigning on low taxes may have worked for Republicans at one point, but times have changed.  Carter, Mondale, and Dukakis all lost because they campaigned on New Deal liberalism after its time was up.  Republicans shouldn't make the same mistake by campaigning on Reaganite conservatism.  It was made for a different time, and it will not win enough support today.  Instead, Republicans need to run on jobs for American workers, standing up for us on trade, and addressing the opioid crisis.

Trump is considering returning to the TPP, which is a terrible idea and will cut into Republican support in the Rust Belt.  Many working-class Democrats gambled by voting for Trump, and if he fails to deliver, they may not gamble again. 

Immigration is the most important issue for most Republicans and the issue that got Trump elected.  Yet Trump and Republicans in Congress have wasted over a year on secondary issues such as tax cuts.  While illegal immigration to the country dropped after Trump took office, the numbers have since increased.  Trump needs to get serious about immigration.  He and Congress should defund sanctuary states and cities; end chain migration, birthright citizenship, and H1-B visas; implement E-Verify; and drastically reduce immigration.  Most importantly, the wall must be built.  That was Trump's biggest campaign promise.  If he can't keep that, how can he be expected to keep any of his other promises?

Congress should pass the Goodlatte bill, which is flawed but the best Republicans can hope for.

This November, Republicans ought to run on reducing immigration.  They should portray the Democratic Party as the party of illegal aliens and say they care more about them than American citizens.

Republicans should also run on the possibility of Trump being impeached if they lose Congress.  This will rile up Trump's base and scare some people into voting in the midterms.  If Trump is impeached or forced to resign, that will be bad for Democrats, because it will make Republicans angry, and they will vote in large numbers in 2020.  Mike Pence would almost certainly be elected to a second term, because Americans won't be ready for three presidents in such a short period of time.  This is one of the reasons Lyndon B. Johnson defeated Barry Goldwater in a landslide in 1964: because Americans didn't want to change presidents so soon after the assassination of John F. Kennedy. 

While a blue wave is probable, it is not inevitable.  The Democratic Party is much more divided than it appears, and these divisions are quite deep and will have ramifications in the future.  The most significant split was seen during the 2016 Democratic primaries between Hillary Clinton-supporters and Bernie Sanders-supporters.  Much of the divide was racial in nature.  Sanders won the white vote, and Clinton won the nonwhite vote.  Clinton-supporters accused Sanders-supporters of ignoring race in favor of class and other forms of inequality, and of being too white and too male.  Sanders-supporters accused Clinton of being a corporatist shill.  The two factions are still vying for control of the Democratic Party.  Their disagreements have temporarily been set aside since both factions despise Trump, but those disagreements still exist, and Trump won't be in the White House forever. 

Democrats don't have a positive message, only a negative one: that Trump is bad.  They don't stand for anything, only against something.

In order to win, Republicans need Trump-like candidates who appeal to the working class.  In order to win, Democrats need centrist candidates who appeal to independents and moderate Republicans.  In both the Alabama Senate and Pennsylvania House elections, the Republican candidate lost to a centrist Democrat by a small margin.  But the Democratic base is farther to the left than most Democratic candidates.  The Democratic Socialists of America, a hard left organization, has been running candidates who have won several primaries.  DSA candidates may appeal to the Democratic base, but they won't appeal to centrists, who are crucial to Democratic electoral success.  If Democrats go too far to the left, they won't get their blue wave, because the centrists and moderate Republicans who otherwise would have voted for them will either vote Republican or stay home.

Midterms tend to have low turnout, which favors the Republicans.  Recently, the Democratic lead in the midterms has been decreasing, while Trump's approval rating has been increasing.

All this bodes well for Republican chances in November.  Still, Republicans should err on the side of caution.