This was expected to be an easier year for Senate Republicans.

Democrats were supposed to be playing defense as Senate candidates ran in conservative states that President Trump handily won two years ago.

But for Republican leaders seeking to maintain control of the Senate, some races are becoming a little too close for comfort.

A prime example is Texas Sen. Ted Cruz, a former presidential candidate who is now fighting to hold on to his seat.

“We’ve got a fight on our hands,” Cruz said. “The extreme left, they’re angry, they’re energized and they are filled with hatred."

Money has poured in to Texas to benefit his challenger, U.S. Rep. Beto O’Rourke, D-El Paso, who is attracting large crowds at rallies.

"It's about the future of this country, the big things we want to do, going from the least insured state in the country to the one that leads on universal healthcare," O’Rourke told supporters at a recent campaign stop.

A national Republican source said while O’Rourke is getting attention, he likely won’t win.

“Beto’s fundraising is obviously nothing to downplay, but it’s still Texas,” the source said. “I think the more his record is litigated… and folks learn more about his anti-gun, open borders record the gap grows.”

In addition to Texas, Real Clear Politics lists eight other Senate races as tossups—Arizona, Indiana, Montana, Missouri, Florida, Tennessee, Nevada and North Dakota.

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Some involve red state incumbent Democrats such as Joe Donnelly in Indiana, Claire McCaskill in Missouri, and Heidi Heitkamp in North Dakota.

But if Texas and Tennessee, traditional Republican strongholds, are in the mix – then there is a possibility that Democrats could have a path to reclaim the Senate.

Part of Donnelly’s pitch is he’s not entirely anti-President Trump.

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“Hoosiers want a senator who works for them. Now, I'll work with any president, but I don't work for any president,” Donnelly told Fox News. “I work for the people of Indiana.”

Democrats are expressing hope the Senate majority is in play – energized by the numbers in Texas, Tennessee, and other places.

But they acknowledge their incumbent senators must perform in what are expected to be hard-fought races.

“North Dakota, Missouri and Florida – three very close, very tough fights in very tough states for three members of the Senate, two of whom at least won during Obama's last election, where they had the benefit of him being at the top of the ticket,” Democratic strategist Mary Anne Marsh told Fox News.

Marsh said Democrats even have a chance in states that are Republican strongholds.

“For the first time, not only do you have Democrats defending red states, there are some Dems who could win some red states like Tennessee, like Texas and don't forget Mississippi. [Former Rep.] Mike Espy has a really good chance of winning [in Mississippi],” Marsh said.

Sources close to Majority Leader Mitch McConnell acknowledge a tough election environment. But they suggest a GOP win in North Dakota is quite possible, and they don’t believe they will lose the majority in the Senate.