Some people might conclude that Republicans are insulated because the mid-term electorate favors them. That's not exactly true. The mid-term electorate is more favorable to the GOP than the Presidential year electorate. That doesn't mean the electorate will be favorable to the Republicans. In mid-terms swing voters heavily swing to the out of power party, while the out of party power's supporters are energized to vote. A more favorable electorate didn't help the Republicans in 2006.
Right now Donald Trump isn't any more unpopular than he was when he was elected. Is his unpopularity assured? Based on recent history it appears that way, but there were reasons the parties were unpopular. In 2006 America didn't like Republicans due to Katrina, the Iraq War, and Republican corruption.
In 2008, Democrats got arrogant with their majorities. At first it appeared the two parties would work together on the stimulus. They were consulting with Republicans. In a meeting with the President Republican whip Eric Cantor objected to items in the President's package. President Obama told Cantor, "I won." He implied that since he won, America wanted what he was putting in the package, and that Republicans either went along with what he put in the stimulus or they'd be left out entirely. Republicans chose to be left out entirely and the stimulus passed without a single Republican vote.
During the next two years Democrats passed broad sweeping legislation that contained things Republicans wouldn't vote for. These bills included the Affordable Care Act, Obamacare. The Democrats thought that by passing bills Republicans wouldn't vote for would increase their popularity and make the Republicans look obstructionist. The opposite happened. Passing partisan bills galvanized Republicans against the Democrats and swung swing votes to the GOP. This energy was repeated in Barack Obama's second mid-term in 2014.
The lesson here is that Republicans and Donald Trump winning the election doesn't make them popular or mean America endorsed everything they wanted to do to the exclusion of the Democrats. If the Republicans arrogantly pass bills too conservative for Democrats to vote for them then they too will have a poor mid-term.
I'm not saying you can't pass any partisan bills. Barack Obama admitted later it would've been smarter to break up the stimulus into several bills, with one or more containing only tax cuts. Republicans would've been on board with a tax cut bill and the GOP voting for some of the President's bills might've softened opposition to him and might not have energized opposition that became the Tea Party. The lesson is to be cautious and judicious with the partisan bills that you'll pass along party lines. If not, Democrats will take the House in 2018.