What does "talking up the threat of impeachment to motivate their base" mean?
Especially "motivate their base"??

Context>>>>>>>>>>>>>>>>>>>>>>>>>>
Republicans facing bad news in House generic ballot polls and worse news from actual special election results have found a new thread of hope: If President Donald Trump’s unpopularity is the source of their problems, then perhaps rank-and-file Democrats’ zeal to remove him from office can be their salvation.

Starting earlier this month, GOP groups have been talking up the threat of impeachment to motivate their base, and Democratic Party leaders have tried to avoid talking about it.

Conservative pundits, meanwhile, are salivating over polling from Quinnipiac that shows impeachment to be a true wedge issue that commands overwhelming support from rank-and-file Democrats while the mass public expresses profound unease.