Republicans on Monday forced Democrats to re-open the government. But they haven't gotten what they want, either – which is why resolving the next shutdown may be harder.

Democrats want legal protection for hundreds of thousands of "Dreamers" under President Barack Obama's Deferred Action for Childhood Arrivals program. They failed to get it from the current, three-day government shutdown.

Republicans want a big boost in defense spending beyond the limitations of caps in current law. Yet that wasn't part of the temporary agreement between Senate Republican and Democratic leaders that ends the shutdown.

With every passing week, the absence of a Pentagon deal generates more pressure from Defense Secretary James Mattis and national security conservatives who call the requested increases vital for the nation's readiness. As a result, some Republicans may soon join Democrats in preferring a shutdown to a mere extension of government funding at existing levels.

The defense spending issue played a small role in weekend debate over the shutdown. Democrats used the drama of the shutdown to take a stand on DACA, hoping to pressure President Donald Trump and his party to accept a bipartisan solution.

To the chagrin of some House and Senate liberals, Republicans made Democrats back down by pressing for a simple extension of government funding at existing levels. Instead of continuing to hold out, Senate Minority Leader Chuck Schumer decided to test Republican counterpart Mitch McConnell's pledge for even-handed floor debate of an issue on which Democrats hold the high ground in public opinion.

The risks of coming up empty-handed are obvious. Even success in the Senate provides no assurance of corresponding action in the House.

But if the DACA effort fails, Republicans themselves will face pressure for a different shutdown strategy the second time around.

Simple funding extensions to keep government up and running provide no extra money for the Pentagon. So the GOP's strong desire for that extra money, over time, diminishes the usefulness of simple extensions as a tool to pressure Democrats.

Behind the scenes, the two parties have actually drawn close to a spending agreement. Democrats insist non-defense programs receive boosts nearly comparable to the Pentagon's. Weary just like Democrats of austerity imposed by a 2011 spending-cut agreement, Republicans are willing to deal.

But Democrats, even in surrendering Monday, haven't abandoned their position that any spending deal requires agreement on other outstanding issues, too. Without a DACA fix, they'll still have the power to shut down the government when the new compromise expires Feb. 8.

Only this time, they may have company from pro-defense Republicans unwilling to kick the Pentagon-spending can further down the road.

That could generate election-year pressure on Trump and congressional leaders for a negotiated solution from both ends of the ideological spectrum. It could also entrench both sides for a longer shutdown battle than the one drawing to a close Monday.