EXPLAINER-Five reasons why Congress is struggling to strike immigration deal as shutdown approaches

The U.S. ​Senate on Thursday

blocked legislation that would fund the Department of Homeland ​Security past a Friday deadline, as Democrats pressed ‌to ​rein in the Trump administration's immigration crackdown.

Here are five difficult topics Republicans and Democrats are grappling with as they try to reach a deal that would avert a shutdown: NEW CONTROLS ON HOW ICE AND ‌CBP AGENTS OPERATE

Democrats in the Senate and House of Representatives want Immigration and Customs Enforcement and Customs and Border Protection agents -- especially those on roving patrols -- to shed their face masks and wear legible name and badge IDs. They also want agents to wear body cameras and procedures written into ‌law making camera footage available during investigations of conduct. Other Democratic demands include requiring judicial warrants before DHS officers can enter private property.

Republicans argue ‌Democrats' constraints could endanger agents or their families, while Democrats say these are long-held practices police departments and other law enforcement forces abide by. NEW CONTROLS ON WHERE ICE AND CBP OPERATE

Democrats say no more ICE or CBP agents hanging out at churches, schools, hospitals, voting places and courts to try to nab immigrants. TIGHTER 'SAFEGUARDS' ON DETENTION FACILITIES

DHS facilities ⁠that hold ​migrants must grant immediate access to detainees' ⁠lawyers to prevent U.S. citizens from arrest or detention, Democrats argue. They also want to end impediments they say the Trump administration erects when members of Congress try to ⁠visit detention centers as part of their oversight powers. REPUBLICAN DEMANDS FOR SAFEGUARDING FEDERAL AGENTS

Democrats focus on safeguarding the public from what they see as overzealous ICE ​and CBP operations that have seen the killings of two U.S. citizens and growing public backlash in cities throughout the country. Republicans ⁠are focused on providing safety for federal agents to carry out arrests and deportations of immigrants in the country illegally, as ordered by President Donald Trump. Doing so will make ⁠American ​towns and cities safer, they argue. They want new provisions in a $64.4 billion DHS funding bill to punish "sanctuary cities" that do not work in tandem with federal agents on immigration enforcement activities.

There is no legal definition for what constitutes a sanctuary jurisdiction and courts have ruled that ⁠state and local governments cannot be compelled to enforce federal regulatory programs. Nor can the federal government withhold funds to localities to coerce them ⁠to cooperate. THE CLOCK AND THE CALENDAR

The ⁠Friday deadline means negotiators only had two weeks to discuss these and other proposals. Democrats have argued that should be sufficient time. Republicans maintain this is too complex to resolve in that timeframe and then ‌put any deal into legislative ‌language and sell it to rank-and-file lawmakers.