WASHINGTON >> Eager to focus voters on immigration in the lead-up to the midterm elections, President Donald Trump today escalated his threats against a migrant caravan trudging slowly toward the U.S. border as the Pentagon prepared to deploy thousands of U.S. troops to support the border patrol.

Trump tweeted: “This is an invasion of our Country and our Military is waiting for you!”

His warning came as the Pentagon began executing a support mission dubbed Operation Faithful Patriot to provide military assistance requested by the Customs and Border Patrol. Two U.S. officials said the troop total was likely to be slightly above 5,000, with troops coming mainly from major Army bases from coast to coast. The officials spoke on condition of anonymity to discuss a troop plan that was not yet publicly announced.

The Customs and Border Patrol is pushing a surge in personnel in response to the caravan of Central American immigrants, which was still hundreds of miles from the U.S. border, three administration officials said. The military troops are intended to assist the border patrol, not engage directly with migrants, several officials said.

The White House is also weighing additional border security measures, including blocking those traveling in the caravan from seeking legal asylum and keeping them from entering the U.S.

The escalating rhetoric and expected deployments come as the president has been trying to turn the caravan into a key election issue with just days to go before the midterm elections that will determine whether Republicans maintain control of Congress.

“This will be the election of the caravans, the Kavanaughs, law and order, tax cuts, and you know what else? It’s going to be the election of common sense,” Trump said at a rally in Illinois on Saturday night.

He continued his threats today, tweeting, without providing evidence, that, “Many Gang Members and some very bad people are mixed into the Caravan heading to our Southern Border.”

“Please go back,” he urged them, “you will not be admitted into the United States unless you go through the legal process. This is an invasion of our Country and our Military is waiting for you!”

A possible announcement by Trump on the other border measures had been tentatively slated for Tuesday, administration officials had said, but he is instead traveling to Pittsburgh, where a gunman massacred 11 people at a synagogue Saturday in what is believed to be the deadliest attack on Jews in U.S. history. Spokeswoman Sarah Huckabee Sanders said today pushed off questions about the caravan and possible border measures.

“We have a number of options on the table,” she said, adding she’d let the public know of any upcoming immigration speeches but she was unaware of any right now.

The Wall Street Journal was the first to report the planned deployment, first announced late last week, was likely to be much larger than the preliminary figures of 800 to 1,000 troops. The Journal reported that the Pentagon plans to deploy 5,000 troops, mainly military police and engineers.

The troops are expected to perform a wide variety of functions such as transporting supplies for the Border Patrol, but not engage directly with migrants seeking to cross the border from Mexico, officials said. One U.S. official said the troops will be sent initially to staging bases in California, Texas and Arizona while the CBP works out precisely where it wants the troops positioned. U.S. Transportation Command posted a video on its Facebook page today of a C-17 transport plane that it said was delivering Army equipment to the Southwest Border in support of Operation Faithful Patriot.

National Guard troops routinely perform those same functions, so it remains unclear clear why active duty forces would be used. The National Guard is often used by states to help with border security. But active duty troops are rarely deployed within the United States except for domestic emergencies like hurricanes or floods.

The U.S. military has already begun delivering jersey barriers to the southern border in conjunction with the deployment plans.

Mattis told reporters traveling with him Sunday that the deployment was still being worked out, but that the additional troops would provide logistical and other support to the Border Patrol and bolster the efforts of the approximately 2,000 National Guard forces already there. That includes functions such as air support and equipment, including vehicles and tents.

Trump has spent the last week trying to call attention to the caravan traveling by foot through Mexico. It remains hundreds of miles from U.S. soil.