(CNN) Red-state Democrats running for Senate in 2018 cautiously backed President Donald Trump's decision to approve targeted strikes in Syria. But now that the strikes have happened, almost all are urging the President to make his future plans in Syria clear and come to Congress for approval.

The Democratic support ranges from full-throated endorsements to tepid backing, but most Democrats running for the Senate in 2018 for now back the strikes.

The skeptical backing by Democrats charting runs against Trump's Republican Party in 2018 stands in contrast with the majority of Republicans who have backed the strikes wholeheartedly, using them as a sign that Trump will take action where past Democrats -- namely former President Barack Obama -- failed.

Sen. Bill Nelson, a Florida Democrat who is facing an pricey and competitive race against Gov. Rick Scott, tweeted Saturday night that he supports the attack "because Assad must be held accountable for the use of chemical weapons," referring to Syrian President Bashar al-Assad.

Sen. Joe Donnelly, one of the most vulnerable Democrat running in 2018, said in a statement that he supports the "international military response, which demonstrates that there are consequences for using chemical weapons on innocent civilians."

He added: "Now, I want to hear from the president, the military and our diplomatic leaders on the strategy moving forward."

And Rep. Kyrsten Sinema, the Arizona Democrat running for Senate, backed the strikes as an important message "that the use of these heinous weapons will not be tolerated," but later said Trump now must "work with Congress to develop a clear, unified and effective strategy to end the conflict in Syria."

Hours after the strikes, the Trump administration pledged future action in Syria if Assad continues to use chemical weapons.

"If the Syrian regime uses this poisonous gas again, the United States is locked and loaded," US Ambassador to the United Nations Nikki Haley said Saturday. "When our President draws a red line, our President enforces a red line."

Most of the 2018 Democrats are demanding that Trump come to Congress before striking to Syria again. But Sen. Tim Kaine, a safer Virginia Democrat who is running for reelection in 2018, blasted Trump's decision to strike Syria without congressional approval.

"President Trump's decision to launch airstrikes against the Syrian government without Congress's approval is illegal and -- absent a broader strategy -- it's reckless," Kaine said. "Last week, President Trump was adamant that the U.S. was leaving Syria imminently. This week, he is opening a new military front."

He added: "We need to put clear limits in place before he starts another war, and I'm working to do just that."

But Kaine's view was not widely held.

Former Tennessee Gov. Phil Bredesen tweeted that Trump's action was "justified."

"The chemical attacks in Syria compel us to act decisively in cooperation with our allies. If the President intends further action, I trust Congress will take up its Constitutional war-making responsibilities. Godspeed to our military," he wrote.

Sen. Heidi Heitkamp wrote a lengthy Facebook post about the attacks which empathized with the plight of the civilians in Syria and described the images of chemical attack victims as "incredibly sad and disturbing."

Though Heitkamp said, "Assad must be held accountable for his egregious human rights violations and the gassing of his own people — a crime against international law and humanity as well as an act of unspeakable cowardice," she never directly says that she backs the strikes. She does, however, call for Trump to present an "updated, clear strategy that carefully considers the next appropriate military and diplomatic steps while avoiding an extended military conflict."

"Any U.S. military action in the region must be wary of dragging our armed forces into a protracted and broader conflict in the region, especially as our military faces challenges impacting U.S. interests around the globe. Particularly during these fraught times, I'm thinking of our servicemembers both at home and abroad," she wrote. "Going forward, Congress must be involved in decisions about further action and must vote to authorize military force."

In a statement, Ohio Sen. Sherrod Brown described the strikes as a "targeted and proportional response to the Assad regime's gruesome attacks on civilians, and it's important that our allies in Britain and France were part of this process."

But he added that Trump now must "present a long-term strategy to the American people, and he must win their support before taking further military action."

Sen. Tina Smith, who will run in the special election for former Sen. Al Franken's Minnesota seat this year, said "Assad and his supporters must be held accountable for their actions."

"An airstrike launch like this should be done with a clear strategy and with input and authorization from Congress. We have a Constitution," she said, adding, "I don't want to see our country end up in another broad, no-end-in-sight military engagement that puts the lives of servicemembers at risk."