Gov. Larry Hogan has so far declined to bring Maryland into a newly formed alliance of states opposed to President Donald J. Trump's decision to pull the United States out of the Paris climate accord.
A dozen states have joined the newly formed U.S. Climate Alliance of states committed to staying on the path to fight climate change the United States pledged to follow under President Barack Obama. Most are led by Democrats such as Virginia Gov. Terry McAuliffe, who joined the alliance Monday.
McAuliffe said Trump's announcement to withdraw from the Paris agreement "does not speak for the states and cities that are committed to fighting climate change."
"If the federal government insists on abdicating leadership on this issue, it will be up to the American people to step forward — and in Virginia we are doing just that," McAuliffe said.
Hogan has not ruled out joining. Spokeswoman Amelia Chasse said Monday that the administration is "still learning about the initiative." She also said Maryland's air quality goals already surpass those set by the Paris accord.
The Republican governor has reacted testily to suggestions from individuals on his Facebook page that Maryland join the alliance. He accused one who urged him Saturday to take that step of being "not only off topic but ill informed." To another he replied: "We are leading the nation on this subject. Pay attention."
Hogan and McAuliffe are scheduled to appear together Thursday in Annapolis for a meeting of federal, state and local officials overseeing Chesapeake Bay restoration efforts.
The national climate alliance was launched by three Democratic governors — Jerry Brown of California, Andrew Cuomo of New York and Jay Inslee of Washington.
Last week, Charlie Baker of Massachusetts and Phil Scott of Vermont became the first Republicans to align their states with the group.
Like Hogan, Baker and Scott are Republicans who refused to support Trump in his 2016 general election campaign against Democrat Hillary Clinton. But since the election, Baker and Scott have been outspoken critics of Trump policies while Hogan has steered a more cautious course.
Other states that have joined the alliance are Connecticut, Delaware, Hawaii, Minnesota, Oregon, and Rhode Island. Puerto Rico is also a member, and Mayor Muriel Bowser of Washington has also pledged to uphold the terms of the Paris accord.
Hogan has come under pressure from environmental advocates to join the alliance. Mike Tidwell, executive director of the Chesapeake Climate Action Network, said Maryland voters "are overwhelmingly supportive of the Paris Climate Agreement that Trump rejected last week."
"For Governor Hogan, it is imperative that Maryland join other states in rejecting Trump's appalling vision of burning more and more coal and fracked gas in a warming world," Tidwell said in a statement.
At least one of Hogan's potential Democratic challengers took McAuliffe's decision as an opportunity to tweak Hogan for hesitating to join.
Baltimore County Executive Kevin Kamenetz posted a statement on Twitter hailing Virginia's move.
"Glad to see our neighbors in Virginia join the U.S. Climate Alliance. @LarryHogan must defend Maryland's environment! #Act on Climate," Kamenetz tweeted.
U.S. Rep. John K. Delaney, another potential challenger, tweeted that it was "unbelievable that Maryland isn't doing the same."
After Trump announced his decision, a Hogan spokesman offered a measured dissent.
"This is not an action the governor would have taken," spokesman Doug Mayer said.
Since then, Hogan aides have avoided harsher criticism of Trump while emphasizing the governor's record on the environment. Chasse pointed to his signing of the 2016 Greenhouse Gas Reduction Act to accelerate Maryland's greenhouse gas reduction goals. She also noted Hogan's support this year for measures to reduce emissions by promoting electric cars and incentives for using renewable energy.
The spokeswoman said the greenhouse gas law includes "some of the most aggressive air quality goals in the country — significantly more aggressive than those in the Paris accord."
Chasse also pointed out that Maryland is already a member of a multi-state, regional compact, the Regional Greenhouse Gas Initiative, which Maryland joined in 2007 under Democratic Gov. Martin O'Malley. The initiative is a compact of nine Northeast states that require electricity generators to bid for the right to continue emitting carbon. The auctions of those carbon "credits" have yielded millions in proceeds that Maryland has used to provide incentives for installing solar panels and buying more efficient appliances, among other things.
"Governor Hogan remains committed to preserving Maryland's natural resources for future generations, and Maryland will continue to lead by example," Chasse said.
The leaders of the Sierra Club's Maryland chapter said it would send a strong message if Hogan joined the climate alliance. But David Smedick, the organization's Beyond Coal Campaign policy representative, said it's more important that Hogan take action to cap power plant and transportation-related carbon emissions across the Northeast.
Hogan has expressed support for extending the Regional Greenhouse Gas Initiative agreement to 2030, and the administration has also hinted interest in developing an initiative to address pollution from cars and trucks.
"It's time for Governor Hogan to step out and say, 'We're going to strengthen RGGI' or 'How are we going to reduce carbon pollution from vehicles?'" Smedick said.
Hogan's record has been mixed on emissions-related legislation and programs.
While he supported the 2016 greenhouse gas measure, he vetoed legislation passed by the General Assembly last year to increase the amount of renewable energy utilities and electricity suppliers must buy. The legislature overrode the veto this year.
The General Assembly also approved legislation that allows utilities to spend a customer surcharge on energy efficiency programs; it became law without Hogan's signature.
Hogan could face new climate-related challenges from the Democratic-dominated Assembly next year.
Del. Eric Luedtke, a Montgomery County Democrat, said last week that he is likely to submit legislation to bring Maryland into the alliance if Hogan does not do so on his own.
"It's more of the same from Larry Hogan. He's all talk, now walk," Luedtke said.
Baltimore Sun reporter Scott Dance contributed to this article.
An earlier version of this article misstated the number of states that have joined the U.S. Climate Alliance.