We make fun of Nancy Pelosi, but she was a far more effective speaker of the House to push the Obama agenda than Paul Ryan has been to push the Trump agenda.  But in all fairness to the Republican leadership, the Democrats are loyal to their president and vote the straight party line.  A few Democrats like Senator Manchin of West Virginia will make some noise of independence, but when the votes are cast, they do what they're told.

On Sunday, July 30, 2017, Nancy Pelosi said it is "unimportant" for Democrats to win the midterm elections in 2018.

Pelosi is correct.  With John McCain, Susan Collins, and Lisa Murkowski in the Senate, who needs Democrats to stop the Trump agenda?  These "Republicans" voted against repeal of Obamacare.

McCain voted against the Bush tax cuts in 2001, and he will probably vote against the Trump tax cuts just because he is McCain.  McCain's most significant legislation in thirty (30) years as a senator is the McCain-Feingold law, which restricted free speech during elections.  Bush should have vetoed it, but he signed it into law.

In Citizens United v. Federal Election Commission, 558 U.S. 310 (2010), the Supreme Court ruled  that the First Amendment prohibits the  government from restricting independent political expenditures by nonprofit corporations, for-profit corporations, labor unions, and other associations.  The Democrats rail against Citizens United at every opportunity.  But McCain pushed for his law with the liberal Russ Feingold.  McCain attacked the Supreme Court's decision, saying it was the "worst decision ever." This is quite a statement considering the Dred Scott case and Roe v. Wade, among others.

Why should the Dems spend money to win some House seats?

If the House passes a bill the Dems do not like, and with the Republicans having only fifty-two nominal "Republicans" in the Senate, the defection of several "Republicans" will kill the House-passed bill.  This means that McCain has finally achieved his dream of being Mr. Bipartisan, Mr. Reach across the Aisle.  He can block any bill the Democrats do not like.

Since he is at the end of his career, he should do the honest and honorable act: switch his party registration to Democrat and stop pretending he is a Republican.  He will be at home with Nancy Pelosi and Chuck Schumer.