WASHINGTON — Democrats pilloried Republicans for irresponsibly shutting down the government when Barack Obama was president, but as a minority party struggling to show resistance in the era of President Trump, they are now ready to let the lights of government go dark.

A group of prominent Senate Democrats on Monday raised the specter of a shutdown over the funding of President Trump’s proposed wall along the border with Mexico. They also signaled a series of protracted budget battles in Congress over a larger force of immigration officers, what they call a deportation force, and funding for Planned Parenthood. They warned that these would also be “poison pills” that could kill any potential deals to keep the gears of government running normally this year.

In a letter to Senator Mitch McConnell, the Republican majority leader, Senator Chuck Schumer and four other Democratic leaders made clear how far they were prepared to go: “We believe it would be inappropriate to insist on the inclusion of such funding in a must-pass appropriations bill that is needed for the Republican majority in control of the Congress to avert a government shutdown so early in President Trump’s administration.”

Democrats have said little up to now about the possibility of employing the brinkmanship that Republicans used in the fights over the budget and the debt ceiling during the Obama administration. But with Mr. Trump expected to formally outline his 2018 budget priorities for the first time on Thursday and an April 28 deadline looming to fund the government for the rest of this fiscal year, the stakes of failing to reach an agreement are ratcheting up higher.

“Most government shutdowns occur not because of specific funding issues but because of emotions around them,” said Stan Collender, who has worked for Democrats on the House and Senate budget committees. A border wall, he said, “is one of the issues that has the potential for creating those kinds of emotions.”

After promising repeatedly during the presidential campaign that Mexico would pay for the construction of a border wall, Mr. Trump has remained vague since taking office about…