The Democrats have plenty to run on. They have done a good job of finding candidates who fit their district. Connor Lamb for instance.
Voters prefer Democrats on immigration, healthcare and other domestic issues. Republicans and Democrats are neck to neck on taxes.
Those are precisely the issues that caused Hillary to lose. You're delusional if you believe immigration and healthcare are good issues for Dims.
The left forgets that Dem's in their own party wanted nothing to do with Obamacare, in their districts Obamacare was a disaster. So much so that in 2014 when it had become clear to the people that Obama lied his ass off in 2012 Dem's screamed at Obama to go on tv and take the blame for this. He did but it didn't help Dem's got their ass whopped in 2014 over Obamacare.
Republicans have made Obamacare a bigger mess. That is why voters side with Democrats now.