Since the national Republican and Democratic parties divide themselves along ideological lines, American politics has followed a very predictable pattern. It is defined by a punctuated equilibrium.
One party wins total control of Washington and has a brief moment to make a big impact. Inevitably, the party in power messes up and loses control of Congress. This is followed by a period where little happens until the opposition also wins the White House. The other party now has their tiny moment to make their mark-- until they mess up.
The Republicans didn’t win in 1994 -- the Democrats lost. The same is true for the Democrats' 2006 victory and the GOP's 2010 victory.
Each time, the party in power screwed up badly and could have been beaten by a group of monkeys in clown suits. Bill Clinton's job approval rating was terrible heading into the 1994 election, due to failed health care and energy tax plans. In 2006, George W. Bush owned the failed Iraq war and the aftermath of Hurricane Katrina. By 2010, Barack Obama had failed to respond to the massive housing crisis or go after anyone who caused it. People spend a lot of time studying winners to divine the secret to their success, but often the answer is they were just facing super easy opponents.
This is why an opposition party shouldn’t focus on simply winning again at all costs: that is mostly determined by the party in power stumbling. They should focus on what they want to do once they do win. These brief moments when a party has total control are the rare times anything big happens, but it only happens if the party is united behind a set of ideas.
Taking advantage of these moments of total control is also critical because of one other major characteristic of American politics: we almost never reverse legislation. Once a policy is enacted, it tends to stick. No matter how much the opposition rallies against it and promises to repeal, they almost never do.
Democrats in 2008 rallied against the corrupt Medicare Part D law, the Bush tax cuts, and Guantanamo Bay. Yet after they gained power, Obama pushed to keep the corrupt Medicare Part D deals intact, backed a law to save almost all the Bush tax cuts, and never closed Guantanamo. Similarly, the Republican party ran on the promise to “repeal and replace” Obamacare for years, and now their effort is bogged down in the Senate.
Trump has become the poster child for why a party shouldn't do anything to win, just for the sake of winning. With a lack of cohesion and discipline, the GOP is possibly squandering their moment for the next decade.
Democrats have become very focused on beating Trump, but Trump is going to do most of the work defeating Trump. The real focus should be on what they will do in that moment after.