The 2016 map always looked good for Democrats.

But if Donald Trump or Ted Cruz is at the top of the GOP ticket, it looks freaking great for them.

The 2014 midterm was nothing short of a disaster for Democrats, a combination of a dismal map, midterm-election Obama fatigue and shoddy recruitment, that ultimately cost Democrats the Senate and netted Republicans nine seats from North Carolina to Colorado.

In 2016, the tables were expected to turn even before Trump emerged. Now things have gone from bad to awful for Republicans' Senate hopes.

"It creates lots of problems and headaches for Republicans, and Democrats firmly believe that it is going to be a train wreck unlike anything seen in a long time," says Cook Political Report analyst Jennifer Duffy. "I have Democrats talking to me about 8 to 10 seats. I am not there yet."

In 2016, Democrats only have 10 seats to hold on to. Republicans, meanwhile, have 24—seven in states Obama won in both 2008 and 2012. And unlike a midterm election where turnout is anemic and older white voters call the shots, the presidential race is expected to bring more minority and young voters out to to polls.

Kyle Kondik, a congressional race analyst at the University of Virginia's Center for Politics, breaks it down into three categories. There are the hardest seats for Republicans to hold onto; Wisconsin and Illinois, which have trended further to the left in recent years. Then there are races that are more truly toss-ups, places like Florida, New Hampshire, Pennsylvania and Ohio where a presidential race could swing the state one way or the other. And, finally there are a new slew of seats that could be up for grabs if Republicans select a presidential nominee like Trump or Cruz.

Since the cycle started, Democrats have bet they could net four or five seats with a specific eye on Ohio, Wisconsin, Pennsylvania, New Hampshire, Illinois and Florida, but the prospect of Cruz or Trump on the top of the ticket is making them more bullish.

Now, Democrats are seriously looking at expanding their map to North Carolina, Missouri, Arizona, Indiana and even Iowa—states with strong incumbents once viewed as hard to knock off. In Iowa, Democrats successfully recruited former state agricultural secretary and lieutenant Gov. Patty Judge to challenge six-term incumbent Sen. Chuck Grassley.

Grassley has regularly been re-elected with more than 60 percent of the vote, but he appears more vulnerable than in years past both because of the prospect of a Trump nomination and in part because of his intransigence as the Senate's Judiciary Committee chairman to move forward President Obama's Supreme Court Justice nominee Merrick Garland.

US Sen. John McCain is fighting off a challenge from Democrats and Republicans. AP

In Arizona, not only is Sen. John McCain fighting off a primary challenge to his right, early polls indicate Democratic challenger Rep. Ann Kirkpatrick is a formidable foe. A Rocky Mountain Poll released this month showed McCain and Kirkpatrick tied at 42 percent among registered voters in the state.

Republicans are generally regarded of having a crop of strong candidates heading into 2016 unlike in 2012 when a slew of primary insurgent conservatives' blunders cost Republicans the Senate. And their candidates have by and large taken their races seriously, investing time and energy in early fundraising. Yet, it may not matter for pragmatic policy makers like Sens. Rob Portman (R-OH) or Pat Toomey (R-PA). Sometimes (as we saw in 2014) a wave is just too much.

"All the money in the world is not worth what a good presidential candidate would be worth," said Kyle Kondik, political analyst at the University of Virginia. "The members who pay the price for extremism at the top of the ticket are not the extreme members."

In recent weeks, both the Cook Political Report and the University of Virginia's Center for Politics have moved several Senate races in Democrats' direction.

"Considering the rise of Donald Trump, the polarization in U.S. politics, and a higher rate of straight-ticket voting, this could be bad news for the GOP," a team of analysts at the UVA Center for Politics wrote earlier this month when they moved Senate races in Iowa, Pennsylvania, Colorado, North Carolina, Missouri, Ohio and Pennsylvania in the Democrats' direction.

But the more Democrats can win in 2016 the better insulated they will be for the 2018 midterm elections when they face another terrible, no good, Senate map where Democratic senators from North Dakota to West Virginia face re-election.

"They really need to run up the score this year," Kondik said.